having grown up, as * the section has been made from the chart given in the atlas of the voyage of the coquille. the scale is. 57 of an inch to a mile. the height of the island, according to m. lesson, is 4026 feet. the deepest part of the lagoon - channel is 162 feet ; its depth is exaggerated in the woodcut for the sake of clearness. the whole sank down, from a basis formed of other corals and their consolidated fragments. thus the difficulty on this head, which before seemed so great, disappears. as the space between the reef and the subsiding shore continued to increase in breadth and depth, and as the injurious effects of the sediment and fresh water borne down from the land were consequently lessened, the greater number of the channels, with which the reef in its fringing state must have been breached, especially those which fronted the smaller streams, will have become choked up by the growth of coral : on the windward side of the reef, where the coral grows most vigorously, the breaches will probably have first been closed. in barrier - reefs, therefore, the breaches kept open by draining the tidal waters of the lagoon - channel, will generally be placed on the leeward side, and they will still face the mouths of the larger streams, although removed beyond the influence of their sediment and fresh - water ; — and this, it has been shown, is commonly the case. referring to the following diagram, in which the newly - formed barrier - reef is represented by unbroken lines, instead of by dots as in the former woodcut, let the work of subsidence go on, and the doubly - pointed hill will form two small a ' a ' — outer edges of the barrier - reef at the level of the sea. the cocoa - nut trees represent coral - islets formed on the reef. b ' b ' — the shores of the island, generally formed of low alluvial land and of coral detritus from the lagoon - channel. a " a " — the outer edges of the reef now forming an atoll. c ' — the lagoon of the newly - formed atoll. according to the scale, the depth of the lagoon and of the lagoon - channel is exaggerated. islands ( or more, according to the number of the hills ) included within one annular reef. let the island continue subsiding, and the coral - reef will continue growing up on its own foundation, whilst the water gains inch by


exaggerated. islands ( or more, according to the number of the hills ) included within one annular reef. let the island continue subsiding, and the coral - reef will continue growing up on its own foundation, whilst the water gains inch by inch on the land, until the last and highest pinnacle is covered, and there remains a perfect atoll. a vertical section of this atoll is shown in the woodcut by the dotted lines ; — a ship is anchored in its lagoon, but islets are not supposed yet to have been formed on the reef. the depth of the lagoon and the width and slope of the reef, will depend on the circumstances just referred to under barrier - reefs. any further subsidence will produce no change in the atoll, except perhaps a diminution in its size, from the reef not growing vertically upwards ; but should the currents of the sea act violently on it, and should the corals perish on part or on the whole of its margin, changes would result during subsidence which will be presently noticed. i may here observe, that a bank either of rock or of hardened sediment, level with the surface of the sea, and fringed with living coral, would ( if not so small as to allow the central space to be quickly filled up with detritus ) by subsidence be converted immediately into an atoll, without passing, as in the case of a reef fringing the shore of an island, through the intermediate form of a barrier - reef. if such a bank lay a few fathoms submerged, the simple growth of the coral ( as remarked in the third chapter ) without the aid of subsidence, would produce a structure scarcely to be distinguished from a true atoll ; for in all cases the corals on the outer margin of a reef, from having space and being freely exposed to the open sea, will grow vigorously and tend to form a continuous ring, whilst the growth of the less massive kinds on the central expanse, will be checked by the sediment formed there, and by that washed inwards by the breakers ; and as the space becomes shallower, their growth will, also, be checked by the impurities of the water, and probably by the small amount of food brought by the enfeebled currents, in proportion to the surface of living reefs studded with innumerable craving mouths : the subsi - dence of a reef based on a bank of this kind, would give depth to its central expanse or lagoon, steepness to its flanks,


in proportion to the surface of living reefs studded with innumerable craving mouths : the subsi - dence of a reef based on a bank of this kind, would give depth to its central expanse or lagoon, steepness to its flanks, and through the free growth of the coral, symmetry to its outline : — i may here repeat that the larger groups of atolls in the pacific and indian oceans cannot be supposed to be founded on banks of this nature. if, instead of the island in the diagram, the shore of a continent fringed by a reef had subsided, a great barrier - reef, like that on the n. e. coast of australia, would have necessarily resulted ; and it would have been separated from the main land by a deep - water channel, broad in proportion to the amount of subsidence, and to the less or greater inclination of the neighbouring coast - land. the effect of the continued subsidence of a great barrier - reef of this kind, and its probable conversion into a chain of separate atolls, will be noticed, when we discuss the apparent progressive disseverment of the larger maldiva atolls. we now are able to perceive that the close similarity in form, dimensions, structure, and relative position ( which latter point will hereafter be more fully noticed ) between fringing and encircling barrier - reefs, and between these latter and atolls, is the necessary result of the transformation, during subsidence, of the one class into the other. on this view, the three classes of reefs ought to graduate into each other. reefs having an intermediate character between those of the fringing and barrier classes do exist ; for instance, on the s. w. coast of madagascar, a reef extends for several miles, within which there is a broad channel from seven to eight fathoms deep, but the sea does not deepen abruptly outside the reef. such cases, however, are open to some doubts, for an old fringing reef, which had extended itself a little on a basis of its own formation, would hardly be distinguishable from a barrier - reef, produced by a small amount of subsidence, and with its lagoon - channel nearly filled up with sediment during a long stationary period. between barrier - reefs, encircling either one lofty island or several small low ones, and atolls including a mere expanse of water, a striking series can be shown : in proof of this, i need only refer to the first plate at the


- reefs, encircling either one lofty island or several small low ones, and atolls including a mere expanse of water, a striking series can be shown : in proof of this, i need only refer to the first plate at the end of this volume, which speaks more plainly to the eye, than any description could to the ear. the authorities from which the charts have been engraved, together with some remarks on them, are given on a separate page descriptive of the plates. at new caledonia ( plate ii. fig. 5. ) the barrier - reefs extend for 150 miles on each side of the submarine prolongation of the island ; and at their northern extremity they appear broken up and converted into a vast atoll - formed reef, supporting a few low coral - islets : we may imagine that we here see the effects of subsidence actually in progress, — the water always encroaching on the northern end of the island, towards which the mountains slope down, and the reefs steadily building up their massive fabrics in the lines of their ancient growth. we have as yet only considered the origin of barrier - reefs and atolls in their simplest form ; but there remain some peculiarities in structure and some special cases, described in the two first chapters, to be accounted for by our theory. these consist, — in the inclined ledge terminated by a wall, and sometimes succeeded by a second ledge with a wall, round the shores of certain lagoons and lagoon - channels ; a structure which cannot, as i endeavoured to show, be explained by the simple growing powers of the corals, — in the ring or bason - like form of the central reefs, as well as of the separate marginal portions of the northern maldiva atolls, — in the submerged condition of the whole, or of parts of certain barrier and atoll - formed reefs ; where only a part is submerged, this being generally to leeward, — in the apparent progressive disseverment of some of the maldiva atolls, — in the existence of irregularly formed atolls, some being tied together by linear reefs, and others with spurs projecting from them, — and, lastly, in the structure and origin of the great chagos bank. step - formed ledges round certain lagoons. — if we suppose an atoll to subside at an extremely slow rate, it is difficult to follow out the complex results. the living corals would grow up on the outer margin ; and likewise probably in the gullies


round certain lagoons. — if we suppose an atoll to subside at an extremely slow rate, it is difficult to follow out the complex results. the living corals would grow up on the outer margin ; and likewise probably in the gullies and deeper parts of the bare surface of the annular reef ; the water would encroach on the islets, but the accumulation of fresh detritus might possibly prevent their entire submergence. after a subsidence of this very slow nature, the surface of the annular reef sloping gently into the lagoon, would probably become united with the irregular reefs and banks of sand, which line the shores of most lagoons. should, however, the atoll be carried down by a more rapid movement, the whole surface of the annular reef, where there was a foundation of solid matter, would be favourably circumstanced for the fresh growth of coral ; but as the corals grew upwards on its exterior margin, and the waves broke heavily on this part, the increase of the massive polypifers on the inner side would be checked from the want of water. consequently, the exterior parts would first reach the surface, and the new annular reef thus formed on the old one, would have its summit inclined inwards, and be terminated by a subaqueous wall, formed by the upward growth of the coral ( before being much checked ), from the inner edge of the solid parts of the old reef. the inner portion of the new reef, from not having grown to the surface, would be covered by the waters of the lagoon. should a subsidence of the same kind be repeated, the corals would again grow up in a wall, from all the solid parts of the resunken reef, and, therefore, not from within the sandy shores of the lagoon ; and the inner part of the new annular reef would, from being as before checked in its upward growth, be of less height than the exterior parts, and therefore would not reach the surface of the lagoon. in this case the shores of the lagoon would be surrounded by two inclined ledges, one beneath the other, and both abruptly terminated by subaqueous cliffs. * * according to mr. couthouy ( p. 26 ) the external reef round many atolls descends by a succession of ledges or terraces. he attempts, i doubt whether successfully, to explain this structure somewhat in the same manner as i have attempted, with respect to the internal ledges round the lagoons


the external reef round many atolls descends by a succession of ledges or terraces. he attempts, i doubt whether successfully, to explain this structure somewhat in the same manner as i have attempted, with respect to the internal ledges round the lagoons of some atolls. more facts are wanted regarding the nature both of the interior and exterior step - like ledges : are all the ledges, or only the upper ones, covered with living coral? if they the ring or bason - formed reefs of the northern maldiva atolls. — i may first observe, that the reefs within the lagoons of atolls and within lagoon - channels, would, if favourably circumstanced, grow upwards during subsidence in the same manner as the annular rim ; and, therefore, we might expect that such lagoon - reefs, when not surrounded and buried by an accumulation of sediment more rapid than the rate of subsidence, would rise abruptly from a greater depth than that at which the efficient polypifers can flourish : we see this well exemplified in the small abruptly - sided reefs, with which the deep lagoons of the chagos and southern maldiva atolls are studded. with respect to the ring or bason - formed reefs of the northern maldiva atolls, it is evident, from the perfectly continuous series which exists, that the marginal rings, although wider than the exterior or bounding reef of ordinary atolls, are only modified portions of such a reef ; it is also evident that the central rings, although wider than the knolls or reefs which commonly occur in lagoons, occupy their place. the ring - like structure has been shown to be contingent on the breaches into the lagoon being broad and numerous, so that all the reefs which are bathed by the waters of the lagoon, are placed under nearly the same conditions with the outer coast of an atoll standing in the open sea. hence the exterior and living margins of these reefs must have been favourably circumstanced for growing outwards, and increasing beyond the usual breadth ; and they must likewise have been favourably circumstanced for growing vigorously upwards, during the subsiding movements, to which by our theory the whole archipelago has been subjected ; and subsidence with this upward growth of the margins would convert the central space of each little reef into a small lagoon. this, however, could only take place with those reefs, which had increased to a breadth sufficient to prevent their central spaces from being almost immediately filled up with the sand and detrit


would convert the central space of each little reef into a small lagoon. this, however, could only take place with those reefs, which had increased to a breadth sufficient to prevent their central spaces from being almost immediately filled up with the sand and detritus are all covered, are the kinds different on the ledges according to the depth? do the interior and exterior ledges occur together in the same atolls ; if so, what is their total width, and is the intervening surface - reef narrow, & c.? driven inwards from all sides : hence it is that few reefs, which are less than half a mile in diameter, even in the atolls where the bason - like structure is most strikingly exhibited, include lagoons. this remark, i may add, applies to all coral - reefs, wherever found. the bason - formed reefs of the maldiva archipelago may, in fact, be briefly described, as small atolls formed during subsidence over the separate portions of large and broken atolls, in the same manner as these latter were formed over the barrier - reefs, which encircled the islands of a large archipelago now wholly submerged. submerged and dead reefs. — in the second section of the first chapter, i have shown that there are in the neighbourhood of atolls, some deeply submerged banks, with level surfaces ; that there are others, less deeply but yet wholly submerged, having all the characters of perfect atolls, but consisting merely of dead coral - rock ; that there are barrier - reefs and atolls with merely a portion of their reef, generally on the leeward side, submerged ; and that such portions either retain their perfect outline, or they appear to be quite effaced, their former place being marked only by a bank, conforming in outline with that part of the reef which remains perfect. these several cases are, i believe, intimately related together, and can be explained by the same means. there, perhaps, exist some submerged reefs, covered with living coral and growing upwards, but to these i do not here refer. as we see that in those parts of the ocean, where coral reefs are most abundant, one island is fringed and another neighbouring one is not fringed ; as we see in the same archipelago, that all the reefs are more perfect in one part of it than in another, — for instance, in the southern half compared with the northern half of the maldiva archipelago, and likewise on the outer coasts compared with the inner coasts of the atolls in


the reefs are more perfect in one part of it than in another, — for instance, in the southern half compared with the northern half of the maldiva archipelago, and likewise on the outer coasts compared with the inner coasts of the atolls in this same group, which are placed in a double row ; as we know that the existence of the innumerable polypifers forming a reef, depends on their sustenance, and that they are preyed on by other organic beings ; and, lastly, as we know that some inorganic causes are highly injurious to the growth of coral, it cannot be expected that during the round of change to which earth, air, and water are exposed, the reef - building polypifers should keep alive for perpetuity in any one place ; and still less can this be expected, during the progressive subsidences, perhaps at some periods more rapid than at others, to which by our theory these reefs and islands have been subjected and are liable. it is, then, not improbable that the corals should sometimes perish either on the whole or on part of a reef ; if on part, the dead portion, after a small amount of subsidence, would still retain its proper outline and position beneath the water. after a more prolonged subsidence, it would probably form, owing to the accumulation of sediment, only the margin of a flat bank, marking the limits of the former lagoon. such dead portions of reef would generally lie on the leeward side, * for the impure water and fine sediment would more easily flow out from the lagoon over this side of the reef, where the force of the breakers is less than to windward ; and therefore the corals would be less vigorous on this side, and be less able to resist any destroying agent. it is likewise owing to this same cause, that reefs are more frequently breached to leeward by narrow channels, serving as by ship - channels, than to windward. if the corals perished entirely, or on the greater part of the circumference of an atoll, an atoll - shaped bank of dead rock, more or less entirely submerged, would be produced ; and further subsidence, together with the accumulation of sediment, would often obliterate * mr. lyell, in the first edition of his principles of geology, offered a somewhat different explanation of this structure. he supposes that there has been subsidence ; but he was not aware that the submerged portions of


obliterate * mr. lyell, in the first edition of his principles of geology, offered a somewhat different explanation of this structure. he supposes that there has been subsidence ; but he was not aware that the submerged portions of reef were in most cases, if not in all, dead ; and he attributes the difference in height in the two sides of most atolls, chiefly to the greater accumulation of detritus to windward than to leeward. but as matter is accumulated only on the backward part of the reef, the front part would remain of the same height on both sides. i may here observe that in most cases ( for instance at peros banhos, the gambier group and the great chagos bank ) and i suspect in all cases, the dead and submerged portions do not blend or slope into the living and perfect parts, but are separated from them by an abrupt line. in some instances small patches of living reef rise to the surface from the middle of the submerged and dead parts. its atoll - like structure, and leave only a bank with a level surface. in the chagos group of atolls, within an area of 160 miles by 60, there are two atoll - formed banks of dead rock ( besides another very imperfect one ) entirely submerged ; a third, with merely two or three very small pieces of living reef rising to the surface ; and a fourth, namely peros banhos ( plate i. fig. 9 ), with a portion nine miles in length dead and submerged. as by our theory this area has subsided, and as there is nothing improbable in the death, either from changes in the state of the surrounding sea or from the subsidence being great or sudden, of the corals on the whole, or on portions of some of the atolls, the case of the chagos group presents no difficulty. so far indeed are any of the above - mentioned cases of submerged reefs from being inexplicable, that their occurrence might have been anticipated on our theory ; and as fresh atolls are supposed to be in progressive formation by the subsidence of encircling barrier - reefs, a weighty objection, namely that the number of atolls must be increasing infinitely, might even have been raised, if proofs of the occasional destruction and loss of atolls could not have been adduced. the disseverment of the larger maldiva atolls. — the apparent progressive disseverment in the maldiva archipelago


raised, if proofs of the occasional destruction and loss of atolls could not have been adduced. the disseverment of the larger maldiva atolls. — the apparent progressive disseverment in the maldiva archipelago of large atolls into smaller ones, is, in many respects, an important consideration, and requires an explanation. the graduated series, which marks as i believe this process, can be observed only in the northern half of the group, where the atolls have exceedingly imperfect margins, consisting of detached bason - formed reefs. the currents of the sea flow across these atolls, as i am informed by capt. moresby, with considerable force, and drift the sediment from side to side during the monsoons, transporting much of it seaward ; yet the currents sweep with greater force round their flanks. it is historically known that these atolls have long existed in their present state ; and we can believe, that even during a very slow subsidence they might thus remain, the central expanse being kept at nearly its original depth by the accumulation of sediment. but in the action of such nicely balanced forces during a progressive subsidence, ( like that, to which by our theory this archipelago has been subjected, ) it would be strange if the currents of the sea should never make a direct passage across some one of the atolls, through the many wide breaches in their margins. if this were once effected, a deep - water channel would soon be formed by the removal of the finer sediment, and the check to its further accumulation ; and the sides of the channel would be worn into a slope like that on the outer coasts, which are exposed to the same force of the currents. in fact, a channel precisely like that bifurcating one which divides mahlos mahdoo ( plate ii. fig. 4. ), would almost necessarily be formed. the scattered reefs situated near the borders of the new ocean - channel, from being favourably placed for the growth of coral, would, by their extension, tend to produce fresh margins to the dissevered portions : such a tendency is very evident, ( as may be seen in the large published chart ) in the elongated reefs on the borders of the two channels intersecting mahlos mahdoo. such channels would become deeper with continued subsidence, and probably from the reefs not growing up perpendicularly, somewhat broader. in this case, and more especially if the channels had been formed originally of considerable breadth, the di


that there should be other large islands wholly submerged ; and these, we may now infer, would be surmounted, not by one enormous atoll, but by several large elongated ones, like the atolls in the maldiva group ; and these again, during long periods of subsidence, would sometimes become dissevered into smaller atolls. i may add, that both in the marshall and caroline archipelagoes, there are atolls standing close together, which have an evident relationship in form : we may suppose, in such cases, either that two or more encircled islands originally stood close together, and afforded bases for two or more atolls, or that one atoll has been dissevered. from the position, as well as form, of three atolls in the caroline archipelago ( the namourrek and elato group ), which are placed in an irregular circle, i am strongly tempted to believe that they have originated by the process of disseverment. * * the same remark is, perhaps, applicable to the islands of ollap, fanadik, and tamatam in the caroline archipelago, of which charts irregularly - formed atolls. — in the marshall group, musquillo atoll consists of two loops united in one point ; and menchicoff atoll is formed of three loops, two of which ( as may be seen in fig. 3. plate ii. ) are connected by a mere ribbon - shaped reef, and the three together are 60 miles in length. in the gilbert group some of the atolls have narrow strips of reef, like spurs, projecting from them. there occur also in parts of the open sea, a few linear and straight reefs, standing by themselves ; and likewise some few reefs in the form of crescents, with their extremities more or less curled inwards. now, the upward growth of a barrier - reef which fronted only one side of an island, or one side of an elongated island with its extremities, ( of which cases exist, ) would produce after the complete subsidence of the land, mere strips or crescent or hook - formed reefs : if the island thus partially fronted became divided during subsidence into two or more islands, these islands would be united together by linear reefs ; and from the further growth of the coral along their shores together with subsidence, reefs of various forms might ultimately be produced, either atolls united together by linear reefs, or atolls with spurs projecting from them. some, however,


reefs ; and from the further growth of the coral along their shores together with subsidence, reefs of various forms might ultimately be produced, either atolls united together by linear reefs, or atolls with spurs projecting from them. some, however, of the more simple forms above specified, might, as we have seen, be equally well produced by the coral perishing during subsidence on part of the circumference of an atoll, whilst on the other parts it continued to grow up till it reached the surface. the great chagos bank. — i have already shown that the submerged condition of the great chagos bank, ( plate ii. fig. 1. with its section fig. 2. ) and of some other banks in the chagos group, may in all probability be attributed to the coral having perished before or during the movements of subsidence, to which this whole area by our theory has been sub - are given in the atlas of duperrey ' s voyage : a line drawn through the linear reefs and lagoons of these three islands forms a semicircle. consult also, the atlas of lutke ' s voyage ; and for the marshall group that of kotzebue ; for the gilbert group ( which is referred to in the ensuing page ) consult the atlas of duperrey ' s voyage. most of the points here referred to may, however, be seen in krusenstern ' s general atlas of the pacific. jected. the external rim or upper ledge, ( shaded in the chart, ) consists of dead coral - rock thinly covered with sand ; it lies at an average depth of between five and eight fathoms, and perfectly resembles in form the annular reef of an atoll. the banks of the second level, the boundaries of which are marked by dotted lines in the chart, lie from about fifteen to twenty fathoms beneath the surface ; they are several miles broad, and terminate in a very steep slope round the central expanse. this central expanse i have already described, as consisting of a level muddy flat between thirty and forty fathoms deep. the banks of the second level, might at first sight be thought analogous to the internal step - like ledge of coral - rock which borders the lagoons of some atolls, but their much greater width, and their being formed of sand, are points of essential difference. on the eastern side of the atoll some of the banks are linear and parallel, resembling islets in a great river, and pointed directly towards a


first appeared to me far more anomalous than any i had met with. the process of formation is nearly the same with that, by which mahlos mahdoo has been trisected ; but in the chagos bank the channels of the oceanic currents entering at several different quarters, have united in a central space. this great atoll - formed bank appears to be in an early stage of disseverment ; should the work of subsidence go on, from the submerged and dead condition of the whole reef, and the imperfection of the s. e. quarter, a mere wreck would probably be left. the pitt ' s bank, situated not far southward, appears to be precisely in this state : it consists of a moderately level, oblong bank of sand, lying from 10 to 20 fathoms beneath the surface, with two sides protected by a narrow ledge of rock which is submerged between 5 and 8 fathoms. a little further south, at about the same distance as the southern rim of the great chagos bank is from the northern rim, there are two other small banks with from 10 to 20 fathoms on them ; and not far eastward soundings were struck on a sandy bottom, with between 110 and 145 fathoms. the northern portion with its ledge - like margin, closely resembles any one segment of the great chagos bank, between two of the deep - water channels, and the scattered banks southward appear to be the last wrecks of less perfect portions. i have examined with care the charts of the indian and pacific oceans, and have now brought before the reader all the examples, which i have met with, of reefs differing from the type of the class to which they belong ; and i think it has been satisfactorily shown, that they are all included in our theory, modified by occasional accidents which might have been anticipated as probable. in this course we have seen, that in the lapse of ages encircling barrier - reefs are occasionally converted into atolls, — the name of atoll being properly applicable, at the moment when the last pinnacle of encircled land sinks beneath the surface of the sea. we have, also, seen that large atolls during the progressive subsidence of the areas, in which they stand, sometimes become dissevered into smaller ones ; at other times, the reef - building polypifers having entirely perished, atolls are converted into atoll - formed banks of dead rock ; and these again, through further subsidence and the accumulation


, sometimes become dissevered into smaller ones ; at other times, the reef - building polypifers having entirely perished, atolls are converted into atoll - formed banks of dead rock ; and these again, through further subsidence and the accumulation of sediment, modified by the force of the oceanic currents, pass into level banks with scarcely any distinguishing character. thus may the history of an atoll be followed from its first origin, through the occasional accidents of its existence, to its destruction and final obliteration. objections to the theory of the formation of atolls and barrier - reefs. — the vast amount of subsidence, both horizontally or in area, and vertically or in depth, necessary to have submerged every mountain, even the highest, throughout the immense spaces of ocean interspersed with atolls, will probably strike most people as a formidable objection to my theory. but as continents, as large as the spaces supposed to have subsided, have been raised above the level of the sea, — as whole regions are now rising, for instance, in scandinavia and south america, — and as no reason can be assigned, why subsidences should not have occurred in some parts of the earth ' s crust on as great a scale both in extent and amount as those of elevation, objections of this nature strike me as of little force. the remarkable point is, that movements to such an extent should have taken place within a period, during which the polypifers have continued adding matter on and above the same reefs. another and less obvious objection to the theory will perhaps be advanced from the circumstance, of the lagoons within atolls and within barrier - reefs never having become in any one instance during prolonged subsidences of a greater depth than 60 fathoms, and seldom more than 40 fathoms : but we already admit, if the theory be worth considering, that the rate of subsidence has not exceeded that of the upward growth of the corals on the exterior margin ; we are, therefore, only further required to admit, that the subsidence has not exceeded in rate the filling up of the interior spaces by the growth of the corals living there, and by the accumulation of sediment. as this filling up must take place very slowly within barrier - reefs lying far from the land, and within atolls which are of large dimensions and which have open lagoons with very few reefs, we are led to conclude that the subsidence thus counter - balanced, must have been slow in an extraordinary degree ; — a conclusion which


land, and within atolls which are of large dimensions and which have open lagoons with very few reefs, we are led to conclude that the subsidence thus counter - balanced, must have been slow in an extraordinary degree ; — a conclusion which accords with our only means, namely, with what is known of the rate and manner of recent elevatory movements, of judging by analogy what is the probable rate of subsidence. in this chapter it has, i think, been shown, that the theory of subsidence, which we were compelled to receive from the necessity of giving to the corals, in certain large areas, foundations at the requisite depth, explains both the normal structure and the less regular forms of those two great classes of reefs, which have justly excited the astonishment of all persons who have sailed through the pacific and indian oceans. but further to test the truth of the theory, a crowd of questions will occur to the reader : do the different kinds of reefs, which have been produced by the same kind of movement, generally lie within the same areas? what is their relation of form and position, — for instance, do adjoining groups of atolls, and the separate atolls in these groups, bear the same relation to each other which islands do in common archipelagoes? have we reason to believe, that where there are fringing reefs, there has not lately been subsidence ; or, for it is almost our only way of ascertaining this point, are there frequently proofs of recent elevation? can we by this means account for the presence of certain classes of reefs in some large areas, and their entire absence in others? do the areas which have subsided, as indicated by the presence of atolls and barrier - reefs, and the areas which have remained stationary or have been upraised, as shown by fringing - reefs, bear any determinate relation to each other ; and are the dimensions of these areas such as harmonize with the greatness of the subterranean changes, which, it must be supposed, have lately taken place beneath them? is there any connection between the movements thus indicated, and recent volcanic action? — all these questions ought to receive answers in accordance with the theory ; and if this can be satisfactorily shown, not only is the theory confirmed, but as deductions, the answers are in themselves important. under this latter point of view, these questions will be chiefly considered in the following chapter. * * i may take this opportunity of briefly considering


shown, not only is the theory confirmed, but as deductions, the answers are in themselves important. under this latter point of view, these questions will be chiefly considered in the following chapter. * * i may take this opportunity of briefly considering the appearances, which would probably be presented by a vertical and deep section across a coral formation ( referring chiefly to an atoll ) formed by the upward growth of coral during successive subsidences. this is a subject worthy of attention, as a means of comparison with ancient coral strata. the circumferential parts would consist of massive species, in a vertical position, with their interstices filled up with detritus ; but this would be the part most subject to subsequent denudation and removal. it is useless to speculate how large a proportion of the exterior annular reef would consist of upright coral, and how much of fragmentary rock, for this would depend on many contingencies, — such as on the rate of subsidence, occasionally allowing a fresh growth of coral to cover the whole surface, and on the breakers having force sufficient to throw fragments over this same space. the conglomerate which composes the base of the islets, would ( if not removed by denudation together with the exterior reef on which it rests ) be conspicuous from the size of the fragments, — the different degrees in which they have been rounded, — the presence of fragments of conglomerate torn up rounded and recemented, — and from the oblique stratification. the corals which lived in the lagoon - reefs at each successive level, would be preserved upright, and they would consist of many kinds, generally much branched. in this part, however, a very large proportion of the rock ( and in some cases nearly all of it ) would be formed of sedimentary matter, either in an excessively fine, or in a moderately coarse state, and with the particles almost blended together. the conglomerate which was formed of rounded pieces of the branched corals, on the shores of the lagoon, would differ from that formed on the islets and derived from the outer coast ; yet both might have accumulated very near each other. i have seen a conglomerate limestone from devonshire like a conglomerate now forming on the shores of the maldiva atolls. the stratification taken as a whole, would be horizontal ; but the conglomerate beds resting on the exterior reef, and the beds of sandstone on the shores of the lagoon ( and no doubt on the external flanks ) would probably be divided ( as


. the stratification taken as a whole, would be horizontal ; but the conglomerate beds resting on the exterior reef, and the beds of sandstone on the shores of the lagoon ( and no doubt on the external flanks ) would probably be divided ( as at keeling atoll and at mauritius ) by numerous layers dipping at considerable angles in different directions. the calcareous sandstone and coral rock would almost necessarily contain innumerable shells, echini, and the bones of fish, turtle, and perhaps of birds ; possibly, also, the bones of small saurians, as these animals find their way to the islands far remote from any continent. the large shells of some species of tridacna would be found vertically imbedded in the solid rock, in the position in which they lived. we might expect, also, to find a mixture of the remains of pelagic and littoral animals in the strata formed in the lagoon, for pumice and the seeds of plants are floated from distant countries into the lagoons of many atolls : on the outer coast of keeling atoll, near the mouth of the lagoon, the case of a pelagic pteropodous animal was brought up on the arming of the sounding lead. all the loose blocks of coral on keeling atoll were burrowed by vermiform animals ; and as every cavity, no doubt, ultimately becomes filled with spathose limestone, slabs of the rock taken from a considerable depth, would, if polished, probably exhibit the excavations of such burrowing animals. the conglomerate and fine - grained beds of coral - rock would be hard, sonorous, white, and composed of nearly pure calcareous matter : in some few parts, judging from the specimens at keeling atoll, they would probably contain a small quantity of iron. floating pumice and scoriæ, and occasionally stones transported in the roots of trees ( see my journal of researches, p. 549 ) appear the only sources, through which foreign matter is brought to coral - formations standing in the open ocean. the area over which sediment is transported from coral - reefs must be considerable : capt. moresby informs me that during the change of monsoons, the sea is discoloured to a considerable distance off the maldiva and chagos atolls. the sediment off fringing and barrier coral - reefs must be mingled with the mud, which is brought down from the land, and is transported seaward through the breaches, which occur in front of almost every


land — areas of subsidence elongated, their intersection and alternation with those of elevation — amount, and slow rate of the subsidence — recapitulation. it will be convenient to give here a short account of the appended map ( plate iii. ) ; a fuller one, with the data for colouring each spot, is reserved for the appendix ; and every place there referred to may be found in the index. a larger chart would have been desirable ; but, small as the adjoined one is, it is the result of many months ' labour. i have consulted, as far as i was able, every original voyage and map ; and the colours were first laid down on charts on a larger scale. the same blue colour, with merely a difference in the depth of tint, is used for atolls or lagoon - islands, and barrier - reefs ; for we have seen, that as far as the actual coral - formation is concerned, they have no distinguishing character. fringing - reefs have been coloured red, for between them on the one hand, and barrier - reefs and atolls on the other, there is an important distinction with respect to the depth beneath the surface, at which we are compelled to believe their foundations lie. the two distinct colours, therefore, mark two great types of structure. the dark blue colour represents atolls and submerged annular reefs, with deep water in their centres. i have coloured as atolls, a few low and small coral - islands, without lagoons ; but this has been done only when it clearly appeared that they originally contained lagoons, since filled up with sediment : when there were not good grounds for this belief, they have been left uncoloured. the pale blue colour represents barrier - reefs. the most obvious character of reefs of this class is the broad and deep - water moat within the reef ; but this, like the lagoons of small atolls, is liable to become filled up with detritus and with reefs of delicately - branched corals : when, therefore, a reef round the entire circumference of an island extends very far into a profoundly deep sea, so that it can hardly be confounded with a fringing - reef which must rest on a foundation of rock within a small depth, it has been coloured pale blue, although it does not include a deep - water moat : but this has only been done rarely, and each case is distinctly mentioned in the appendix. the red colour represents reefs, fringing the land quite closely


depth, it has been coloured pale blue, although it does not include a deep - water moat : but this has only been done rarely, and each case is distinctly mentioned in the appendix. the red colour represents reefs, fringing the land quite closely where the sea is deep, and where the bottom is gently inclined extending to a moderate distance from it, but not having a deep - water moat or lagoon like space parallel to the shore. it must be remembered that fringing reefs are frequently breached in front of rivers and valleys by deepish channels, where mud has been deposited. a space of 30 miles in width has been coloured round or in front of the reefs of each class, in order that the colours might be conspicuous on the appended map, which is reduced to so small a scale. the vermilion spots, and streaks, represent volcanos now in action, or historically known to have been so. they are chiefly laid down from von buch ' s work on the canary islands ; and my reasons for making a few alterations are given in the note below. * * i have also made considerable use of the geological part of berghaus ' physical atlas. beginning at the eastern side of the pacific, i have added to the number of the volcanos in the southern part of the cordillera, and have coloured juan fernandez according to observations collected during the voyage of the beagle, ( geol. trans. vol. v. p. 601. ) the uncoloured coasts consist, first and chiefly, of those, where there are no coral - reefs, or such small portions as to be quite insignificant. secondly, of those coasts where there are i have added a volcano to albemarle island, one of the galapagos archipelago, ( the author ' s journal of researches, p. 457 ). in the sandwich group there are no active volcanos, except at hawaii ; but the rev. w. ellis informs me, there are streams of lava apparently modern on maui, having a very recent appearance, which can be traced to the craters whence they flowed. the same gentleman informs me, that there is no reason to believe that any active volcano exists in the society archipelago ; nor are there any known in the samoa or navigator group, although some of the streams of lava and craters there appear recent. in the friendly group, the rev. j. williams says ( narrative of missionary enterprise, p. 29 ) that toofoa and proby islands are active volcanos. i infer from


of the streams of lava and craters there appear recent. in the friendly group, the rev. j. williams says ( narrative of missionary enterprise, p. 29 ) that toofoa and proby islands are active volcanos. i infer from hamilton ' s voyage in the pandora ( p. 95 ), that proby island is synonymous with onouafou, but i have not ventured to colour it. there can be no doubt respecting toofoa ; and captain edwards ( von buch, p. 386 ) found the lava of a recent eruption at amargura still smoking. berghaus marks four active volcanos actually within the friendly group ; but i do not know on what authority : i may mention that maurelle describes latte as having a burnt - up appearance : i have marked only toofoa and amargura. south of the new hebrides lies matthews rock, which is drawn and described as an active crater in the voyage of the astrolabe. between it and the volcano on the eastern side of new zealand, lies brimstone island, which from the high temperature of the water in the crater, may be ranked as active. ( berghaus vorbemerk. 11. lief. s. 56 ). malte brun, vol. xii. p. 231, says that there is a volcano near port st. vincent in new caledonia. i believe this to be an error, arising from a smoke seen on the opposite coast by cook ( 2nd voyage, vol. ii. p. 23 ) which smoke went out at night. the mariana islands, especially the northern ones, contain many craters ( see freycinet ' s hydrog. descript. ) which are not active. von buch, however, states ( p. 462 ) on the authority of la peyrouse, that there are no less than seven volcanos between these islands and japan. gemellli careri ( churchill ' s collect. vol. iv. p. 458 ), says there are two active volcanos in lat. 23° 30 ' and in lat. 24° ; but i have not coloured them. from the statements in beechey ' s voyage ( p. 518, 4to edit. ) i have coloured one in the northern part of the bonin group. m. s. julien has clearly made out from chinese manuscripts not very ancient, ( comptes rendus, 1840, p. 832 ), that there are two active


i have coloured one in the northern part of the bonin group. m. s. julien has clearly made out from chinese manuscripts not very ancient, ( comptes rendus, 1840, p. 832 ), that there are two active volcanos on the eastern side of formosa. in torres straits, on cap island ( 9° 48 ' s. 142° 39 ' e. ) a volcano was seen burning with great violence in 1793 by capt. bampton ( see introduction to flinders ' reefs, but where the sea is very shallow, for in this case the reefs generally lie far from the land, and become very irregular in their forms ; where they have not become irregular, they have been coloured. thirdly, if i had the means of ascertaining the fact, i should not colour a reef merely coating the edges of a submarine crater, or of a level submerged bank ; for such superficial formations differ essentially, even when not in external appearance, from reefs whose foundations as well as superficies have been wholly formed by the growth of coral. fourthly, in the red sea, and within some parts of the east indian archipelago, ( if the imperfect charts of the latter can be trusted, ) there are many scattered reefs, of small size, represented in the chart by mere dots, which rise out of deep water : these cannot be arranged under either of the three classes : in the red sea, however, some of these little reefs, from their position, seem once to have formed parts of a continuous barrier. there exist, also, scattered in the open ocean, some linear and irregularly - formed strips of coral - reef, which, as shown in the last chapter, are probably allied in their origin to atolls ; but as they do not belong to that class, they have not been coloured ; they are very few in number, and of insignificant dimensions. lastly, voyage, p. 41 ). mr. m ' clelland ( report of committee for investigating coal in india, p. 39 ) has shown that the volcanic band passing through barren island must be extended northwards. it appears by an old chart, that cheduba was once an active volcano ; ( see also silliman ' s north american journal, vol. xxxviii. p. 385. ) in berghaus ' phys. atlas, 1840, no. 7 of geological part, a volcano on the coast of pondicherry is said to have burst forth in 1757. ordinaire ( hist.


classified, have been adopted by most voyagers. i may further remark, that the dark blue colour represents land entirely composed of coral - rock ; the pale blue, land with a wide and thick border of coral - rock ; and the red, a mere narrow fringe of coral - rock. looking now at the map under the theoretical point of view indicated in the last chapter, the two blue tints signify that the foundations of the reefs thus coloured have subsided to a considerable amount, at a slower rate than that of the upward growth of the corals ; and that probably in many cases they are still subsiding. the red signifies that the shores which support fringing - reefs have not subsided ( at least to any considerable amount, for the effects of a subsidence on a small scale would in no case be distinguishable ) ; but that they have remained nearly stationary since the period when they first became fringed by reefs ; or that they are now rising or have been upraised, with new lines of reefs successively formed on them : these latter alternatives are obviously implied, as newly - formed lines of shore, after elevations of the land, would be in the same state with respect to the growth of fringing - reefs, as stationary coasts. if during the prolonged subsidence of a shore, coral - reefs grew for the first time on it, or if an old barrier - reef were destroyed and submerged, and new reefs became attached to the land, these would necessarily at first belong to the fringing class, and, therefore, be coloured red, although the coast was sinking : but i have no reason to believe, that from this source of error, any coast has been coloured wrongly with respect to movement indicated. well characterized atolls and encircling barrier - reefs, where several occur in a group, or a single barrier - reef if of large dimensions, leave scarcely any doubt on the mind respecting the movement by which they have been produced ; and even a small amount of subsequent elevation is soon betrayed. the evidence from a single atoll, or a single encircling barrier - reef, must be received with some caution, for the former may possibly be based upon a submerged crater or bank, and the latter on a submerged margin of sediment, or of worn - down rock. from these remarks we may with greater certainty infer that the spaces, especially the larger ones, tinted blue in the map, have subsided, than that the red spaces have remained stationary, or have been upraised. on the grouping


down rock. from these remarks we may with greater certainty infer that the spaces, especially the larger ones, tinted blue in the map, have subsided, than that the red spaces have remained stationary, or have been upraised. on the grouping of the different classes of reefs. — having made these preliminary remarks, i will consider first how far the grouping of the different kinds of coral - islands and reefs is corroborative of the truth of the theory. a glance at the map shows that the reefs, coloured blue and red, produced under widely different conditions, are not indiscriminately mixed together. atolls and barrier - reefs, on the other hand, as may be seen by the two blue tints, generally lie near each other ; and this would be the natural result of both having been produced during the subsidence of the areas in which they stand. thus, the largest group of encircled islands is that of the society archipelago ; and these islands are surrounded by atolls, and only separated by a narrow space from the large group of low atolls. in the midst of the caroline atolls, there are three fine encircled islands. the northern point of the barrier - reef of new caledonia seems itself, as before remarked, to form a complete large atoll. the great australian barrier is described as including both atolls and small encircled islands. capt. king * mentions many atoll - formed and encircling coral - reefs, some of which lie within the barrier, and others may be said ( for instance between lat. 16° and 13° ) to form part of it. flinders † has described an atoll - formed reef in lat. 10°, seven miles long and from one to three broad, resembling a boot in shape, with apparently very deep water within. eight miles westward of this, and forming part of the barrier, lie the murray islands, which are high and are encircled. in the corallian sea, between the two great barriers of australia and new caledonia, there are many low islets and coral - reefs, some of which are annular, or horse - shoe shaped. observing the smallness of the scale of the map, the parallels of latitude being 900 miles apart, we see, that none of the large groups of reefs and islands supposed to have been produced by long - continued subsidence, lie near extensive lines of coast coloured red, which are supposed to have remained stationary since the growth of their reefs, or to have been upraised and new lines of


reefs and islands supposed to have been produced by long - continued subsidence, lie near extensive lines of coast coloured red, which are supposed to have remained stationary since the growth of their reefs, or to have been upraised and new lines of reefs formed on them. where the red and blue circles do occur near each other, i am able, in several instances, to show that there have been oscillations of level, subsidence having preceded the elevation of the red spots ; and elevation having preceded the subsidence of the blue spots ; and in this case the juxta - position of reefs belonging to the two great types of structure, is little surprising. we may, therefore, conclude that the proximity in the same areas of the two classes of reefs, which owe their origin to the subsidence of the earth ' s crust, and their separation from those formed during its stationary or uprising condition, holds good to the full extent, which might have been anticipated by our theory. * sailing directions, appended to vol. ii. of his surveying voyage to australia. † voyage to terra australia, vol. ii. p. 336. as groups of atolls have originated in the upward growth, at each fresh sinking of the land, of those reefs which primarily fringed the shores of one great island, or of several smaller ones ; so we might expect that these rings of coral - rock, like so many rude outline charts, would still retain some traces of the general form, or at least general range, of the land, round which they were first modelled. that this is the case with the atolls in the southern pacific as far as their range is concerned, seems highly probable, when we observe that the three principal groups are directed in n. w. and s. e. lines, and that nearly all the land in the s. pacific ranges in this same direction ; namely, n. western australia, new caledonia, the northern half of new zealand, the new hebrides, saloman, navigator, society, marquesas, and austral archipelagoes : in the northern pacific, the caroline atolls abut against the n. w. line of the marshall atolls, much in the same manner as the e. and w. line of islands from ceram to new britain do on new ireland : in the indian ocean the laccadive and maldiva atolls extend nearly parallel to the western and mountainous coast of india. in most respects, there is a perfect resemblance with


of islands from ceram to new britain do on new ireland : in the indian ocean the laccadive and maldiva atolls extend nearly parallel to the western and mountainous coast of india. in most respects, there is a perfect resemblance with ordinary islands in the grouping of atolls and in their form : thus the outline of all the larger groups is elongated ; and the greater number of the individual atolls are elongated in the same direction with the group, in which they stand. the chagos group is less elongated than is usual with other groups, and the individual atolls in it are likewise but little elongated ; this is strikingly seen by comparing them with the neighbouring maldiva atolls. in the marshall and maldiva archipelagoes, the atolls are ranged in two parallel lines, like the mountains in a great double mountain - chain. some of the atolls, in the larger archipelagoes, stand so near each other, and have such an evident relationship in form, that they compose little sub - groups : in the caroline archipelago, one such sub - group consists of pouynipete, a lofty island encircled by a barrier - reef, and separated by a channel only four miles and a half wide from andeema atoll, with a second atoll a little further off. in all these respects an examination of a series of charts will show how perfectly groups of atolls resemble groups of common islands. on the direct evidence of the blue spaces in the map having subsided during the upward growth of the reefs so coloured, and of the red spaces having remained stationary, or having been upraised. — with respect to subsidence, i have shown in the last chapter, that we cannot expect to obtain in countries inhabited only by semi - civilized races, demonstrative proofs of a movement, which invariably tends to conceal its own evidence. but on the coral - islands supposed to have been produced by subsidence, we have proofs of changes in their external appearance — of a round of decay and renovation — of the last vestiges of land on some — of its first commencement on others : we hear of storms desolating them to the astonishment of their inhabitants : we know by the great fissures with which some of them are traversed, and by the earthquakes felt under others, that subterranean disturbances of some kind are in progress. these facts, if not directly connected with subsidence, as i believe they are, at least show how difficult it would be to discover proofs of such


and by the earthquakes felt under others, that subterranean disturbances of some kind are in progress. these facts, if not directly connected with subsidence, as i believe they are, at least show how difficult it would be to discover proofs of such movement by ordinary means. at keeling atoll, however, i have described some appearances, which seem directly to show that subsidence did take place there during the late earthquakes. vanikoro, according to the chevalier dillon, * * see capt. dillon ' s voyage in search of la peyrouse. m. cordier in his report on the voyage of the astrolabe, ( p. cxi. vol. i. ) speaking of vanikoro, says the shores are surrounded by reefs of madrepore, " qu ' on assure etre de formation tout - a - fait moderne. " i have in vain endeavoured to learn some further particulars about this remarkable passage. i may here add, that according to our theory, the island of pouynipete, ( pl. i. fig. 7. ) in the caroline archipelago, being encircled by a barrier - reef, must have subsided. in the new s. wales lit. advert. feb. 1835, ( which i have seen through the favour of dr. lloghstky, ) there is an account of this island, ( subsequently confirmed by mr. campbell, ) in which it is said, " at the n. e. end, at a place called tamen, there are ruins of a town, now only accessible by boats, the waves reaching to the steps of the houses. " judging from this passage, one would be tempted to conclude that the island must have subsided, since these houses were built. i may, also, here append a statement in malte brun, ( vol. ix. p. 775, given is often violently shaken by earthquakes, and there, the unusual depth of the channel between the shore and the reef, — the almost entire absence of islets on the reef, — its wall - like structure on the inner side, and the small quantity of low alluvial land at the foot of the mountains, all seem to show that this island has not remained long at its present level, with the lagoon - channel subjected to the accumulation of sediment, and the reef to the wear and tear of the breakers. at the society archipelago, on the other hand, where a slight tremor is only rarely felt, the


long at its present level, with the lagoon - channel subjected to the accumulation of sediment, and the reef to the wear and tear of the breakers. at the society archipelago, on the other hand, where a slight tremor is only rarely felt, the shoalness of the lagoon channels round some of the islands, the number of islets formed on the reefs of others, and the broad belt of low land at the foot of the mountains, indicate that, although there must have been great subsidence to have produced the barrier - reefs, there has since elapsed a long stationary period. * without any authority, ) that the sea gains in an extraordinary manner on the coast of cochin china, which lies in front and near the subsiding coral - reefs in the china sea : as the coast is granitic, and not alluvial, it is scarcely possible that the encroachment of the sea can be owing to the washing away of the land ; and if so, it must be due to subsidence. * mr. couthouy states, ( remarks, p. 44, ) that at tahiti and eimeo the space between the reef and the shore has been nearly filled up by the extension of those coral - reefs, which within most barrier - reefs merely fringe the land. from this circumstance, he arrives at the same conclusion as i have done, that the society islands since their subsidence have remained stationary during a long period ; but he further believes that they have recently commenced rising, as well as the whole area of the low archipelago. he does not give any detailed proofs regarding the elevation of the society islands, but i shall refer to this subject in another part of this chapter. before making some further comments, i may observe how satisfactory it is to me, to find mr. couthouy affirming, that " having personally examined a large number of coral - islands, and also residing eight months among the volcanic class, having shore and partially encircling reefs, i may be permitted to state that my own observations have impressed a conviction of the correctness of the theory of mr. darwin. " this gentleman believes, that subsequently to the subsidence by which the atolls in the low archipelago were produced, the whole area has been elevated to the amount of a few feet : this indeed be a remarkable fact ; but as far as i am able to judge, the turning now to the red colour ; as on our map, the areas which have sunk slowly


the whole area has been elevated to the amount of a few feet : this indeed be a remarkable fact ; but as far as i am able to judge, the turning now to the red colour ; as on our map, the areas which have sunk slowly downwards to great depths are many his conclusion are not sufficiently strong. he states that he found in almost every atoll which he visited, the shores of the lagoon raised from 18 to 30 inches above the sea - level, and containing imbedded tridacnæ and corals standing as they grew ; some of the corals were dead in their upper parts, but below a certain line they continued to flourish. in the lagoons, also, he frequently met with clusters of madrepore, with their extremities standing from one inch to a foot above the surface of the water. now, these appearances are exactly what i should have expected, without any subsequent elevation having taken place ; and i think mr. couthouy has not borne in mind the indisputable fact, that corals, when constantly bathed by the surf, can exist at a higher level than in quite tranquil water, as in a lagoon. as long, therefore, as the waves continued at low water to break entirely over parts of the annular reef of an atoll, submerged to a small depth, the corals and shells attached on these parts might continue living at a level above the smooth surface of the lagoon, into which the waves rolled ; but as soon as the outer edge of the reef grew up to its utmost possible height, or if the reef were very broad nearly to that height, the force of the breakers would be checked, and the corals and shells on the inner parts near the lagoon would occasionally be left dry, and thus be partially or wholly destroyed. even in atolls, which have not lately subsided, if the outer margin of the reef continued to increase in breadth seaward, ( each fresh zone of corals rising to the same vertical height as at keeling atoll, ) the line where the waves broke most heavily would advance outwards, and therefore the corals which, when living near the margin, were washed by the breaking waves during the whole of each tide, would cease being so, and would therefore be left on the backward part of the reef standing exposed and dead. the case of the madrepores in the lagoons with the tops of their branches exposed, seems to be an analogous fact, to the great fields of dead but upright corals in


on the backward part of the reef standing exposed and dead. the case of the madrepores in the lagoons with the tops of their branches exposed, seems to be an analogous fact, to the great fields of dead but upright corals in the lagoon of keeling atoll ; — a condition of things which i have endeavoured to show, has resulted from the lagoon having become more and more enclosed and choked up with reefs, so that during high winds, the rising of the tide ( as observed by the inhabitants ) is checked, and the corals, which had formerly grown to the greatest possible height, are occasionally exposed, and thus are killed : and this is a condition of things, towards which almost every atoll in the intervals of its subsidence must be tending. or if we look to the state of an atoll directly after a subsidence of some fathoms, the waves would roll heavily over the entire circumference of the reef, and the surface of the lagoon would like the ocean never be quite at rest, and and large, we might naturally have been led to conjecture, that with such great changes of level in progress, the coasts which have been fringed probably for ages, ( for we have no reason to believe that coral - reefs are of short duration, ) would not have remained all this time stationary, but would frequently have undergone movements of elevation. this supposition, we shall immediately see, holds good to a remarkable extent ; and although a stationary condition of the land can hardly ever be open to proof, from the evidence being therefore the corals in the lagoon, from being constantly laved by the rippling water, might extend their branches to a little greater height than they could, when the lagoon became enclosed and protected. christmas atoll, ( 2° north lat. ) which has a very shallow lagoon, and differs in several respects from most atolls, possibly may have been elevated recently ; but its highest part appears ( couthouy, p. 46 ) to be only ten feet above the sea - level. the facts of a second class, adduced by mr. couthouy, in support of the alleged recent elevation of the low archipelago, are not all ( especially those referring to a shelf of rock ) quite intelligible to me : he believes that certain enormous fragments of rock on the reef, must have been moved into their present position, when the reef was at a lower level ; but here again the force of the breakers on any inner point of


quite intelligible to me : he believes that certain enormous fragments of rock on the reef, must have been moved into their present position, when the reef was at a lower level ; but here again the force of the breakers on any inner point of the reef being diminished by its outward growth without any change in its level, has not, i think, been borne in mind. we should, also, not overlook the occasional agency of waves caused by earthquakes and hurricanes. mr. couthouy further argues, that since these great fragments were deposited and fixed on the reef, they have been elevated ; he infers this from the greatest amount of erosion not being near their bases, where they are unceasingly washed by the reflux of the tides, but at some height on their sides, near the line of high - water mark, as shown in an accompanying diagram. my former remark again applies here, with this further observation, that as the waves have to roll over a wide space of reef before they reach the fragments, their force must be greatly increased with the increasing depth of water as the tide rises, and therefore i should have expected that the chief line of present erosion would have coincided with the line of high - water mark ; and if the reef had grown outwards, that there would have been lines of erosion at greater heights. the conclusion, to which i am finally led by the interesting observations of mr. couthouy, is, that the atolls in the low archipelago have, like the society islands, remained at a stationary level for a long period : and this probably is the ordinary course of events, subsidence supervening after long intervals of rest. only negative, we are, in some degree, enabled to ascertain the correctness of the parts coloured red on the map, by the direct testimony of upraised organic remains of a modern date. before going into the details on this head, ( printed in small type, ) i may mention, that when reading a memoir on coral formations by mm. quoy and gaimard, * i was astonished to find, for i knew that they had crossed both the pacific and indian oceans, that their descriptions were applicable only to reefs of the fringing class ; but my astonishment ended satisfactorily, when i discovered that, by a strange chance, all the islands which these eminent naturalists had visited, though several in number, — namely, the mauritius, timor, new guinea, the mariana and sandwich archipelagoes, could be


is described by capt. beechey, * as being quite flat, and about eighty feet in height ; it is entirely composed of dead corals, forming a honeycombed, but compact rock. in cases like this, of an island having exactly the appearance, which the elevation of any one of the smaller surrounding atolls with a shallow lagoon would present, one is led to conclude ( with little better reason, however, than the improbability of such small and low fabrics lasting, for an immense period, exposed to the many destroying agents of nature ), that the elevation has taken place at an epoch not geologically remote. when merely the surface of an island of ordinary formation is strewed with marine bodies, and that continuously, or nearly so, from the beach to a certain height, and not above that height, it is exceedingly improbable that such organic remains, although they may not have been specifically examined, should belong to any ancient period. it is necessary to bear these remarks in mind, in considering the evidence of the elevatory movements in the pacific and indian oceans, as it does not often rest on specific determinations, and therefore should be received with caution. six of the cook and austral islands ( s. w. of the society group ), are fringed ; of these, five were described to me by the rev. j. williams, as formed of coral - rock, ( associated with some basalt in mangaia ), and the sixth as lofty and basaltic. mangaia is nearly 300 feet high, with a level summit ; and according to mr. s. wilson † it is an upraised reef ; " and there are in the central hollow, formerly the bed of the lagoon, many scattered patches of coral - rock, some of them raised to a height of forty feet. " these knolls of coral - rock were evidently once separate reefs in the lagoon of an atoll. mr. martens, at sydney, informed me that this island is surrounded by a terrace - like plain at about the height of a hundred feet, which probably marks a pause in its elevation. from these facts we may infer, perhaps, that the cook and austral islands have been upheaved at a period probably not very remote. savage island ( s. e. of the friendly group ), is about forty feet in height. forster ‡ describes the plants as already growing out of * beechey ' s voyage in the pacific, p. 46, 4to. edition.


. savage island ( s. e. of the friendly group ), is about forty feet in height. forster ‡ describes the plants as already growing out of * beechey ' s voyage in the pacific, p. 46, 4to. edition. † couthouy ' s remarks, p. 34. ‡ observations made during voyage round the world, p. 147. the dead, but still upright and spreading trees of coral ; and the younger forster * believes that an ancient lagoon is now represented by a central plain : here we cannot doubt that the elevatory forces have recently acted. the same conclusion may be extended, though with somewhat less certainty, to the islands of the friendly group, which have been well described in the second and third voyages of cook. the surface of tongatabou is low and level, but with some parts a hundred feet high ; the whole consists of coral - rock, " which yet shews the cavities and irregularities worn into it by the action of the tides. " † on eoua the same appearances were noticed at an elevation of between 200 and 300 feet. vavao, also, at the opposite or northern end of the group, consists, according to the rev. j. williams, of coral - rock. tongatabou, with its northern extensive reefs, resembles either an upraised atoll with one half originally imperfect, or one unequally elevated ; and anamouka, an atoll equally elevated. this latter island contains ‡ in its centre a salt - water lake, about a mile - and - a - half in diameter, without any communication with the sea, and around it the land rises gradually like a bank : the highest part is only between twenty and thirty feet ; but on this part, as well as on the rest of the land, ( which as cook observes, rises above the height of true lagoon - islands, ) coral - rock like that on the beach, was found. in the navigator archipelago, mr. couthouy § found on manua many and very large fragments of coral at the height of eighty feet, " on a steep hill - side, rising half a mile inland from a low sandy plain abounding in marine remains. " the fragments were embedded in a mixture of decomposed lava and sand. it is not stated whether they were accompanied by shells, or whether the corals resembled recent species ; as these remains were embedded, they possibly may belong to a remote epoch ; but i presume this was not the opinion of


, to the height of 150 feet, by madreporitic strata of a modern date. he mentions similar formations at waigiou, amboina, bourou, ceram, sonda and timor : at this latter place, mm. quoy and gaimard ¶ have likewise described the primitive rocks, as coated to a considerable height with coral. some small islets eastward of timor are said in kolff ' s voyage * * to resemble small coral islets upraised some feet above the sea. dr. macolmson informs me that dr. hardie found in java an extensive formation, containing an abundance of shells, of which the greater part appear to be of existing species. dr. jack † † * voyage de la coquille, part. zoolog. † freycinet ' s voyage autour du monde. see also the hydrographical memoir, p. 215. ‡ kotzebue ' s first voyage. § lutke ' s voyage, vol. ii. p. 304. | | partie zoolog. voyage de la coquille. ¶ ann. des scien. nat., tom. vi. p. 281. * * translated by windsor earl, chapters vi. and vii. † † geolog. transact. 2nd series, vol. i. p. 403. on the peninsula of malacca, in front of pinang, 5° 30 ' n., dr. ward collected some shells, which dr. malcolmson informs me, although not compared with existing species, had a recent appearance. dr. ward describes in this neighbourhood ( trans. asiat. soc. vol. xviii., part 2, p. 166. ) a single water - worn rock, with a conglomerate of sea shells at its base, situated six miles inland, which, according to the traditions of the natives, was has described some upraised shells and corals, apparently recent, on pulo nias off sumatra ; and marsden relates in his history of this great island, that the names of many promontories, show that they were originally islands. on part of the west coast of borneo and at the sooloo islands, the form of the land, the nature of the soil, and the water - washed rocks, present appearances, * ( although it is doubtful whether such vague evidence is worthy of mention, ) of having recently been covered by the sea ; and the inhabitants of the sooloo islands believe that this has been the


and the water - washed rocks, present appearances, * ( although it is doubtful whether such vague evidence is worthy of mention, ) of having recently been covered by the sea ; and the inhabitants of the sooloo islands believe that this has been the case. mr. cuming, who has lately investigated, with so much success, the natural history of the phillippines, found near cabagan, in luzon, about fifty feet above the level of the r. cagayan, and seventy miles from its mouth, a large bed of fossil shells : these, he informs me, are of the same species with those now existing on the shores of the neighbouring islands. from the accounts given us by captain basil hall and captain beechey † of the lines of inland reefs, and walls of coral - rock worn into caves, above the present reach of the waves, at the loo choo islands, there can be little doubt that they have been upraised at no very remote period. dr. davy ‡ describes the northern province of ceylon as being very low, and consisting of a limestone with shells and corals of very recent origin ; he adds, that it does not admit of a doubt that the sea has retired from this district even within the memory of man. there is also some reason for believing that the western shores of india, north of ceylon, have been upraised within the recent period. § once surrounded by the sea. capt. low has also described ( ibid. part i. p. 131. ) mounds of shells lying two miles inland on this line of coast. * notices of the east indian arch., singapore, 1828, p. 6, and append. p. 43. † capt. b. hall, voyage to loo choo, append. pp. xxi. and xxv. capt. beechey ' s voyage, p. 496. ‡ travels in ceylon, p. 13. this madreporitic formation is mentioned by m. cordier in his report to the institute, ( may 4, 1839, ) on the voyage of the chevrette, as one of immense extent, and belonging to the latest tertiary period. § dr. benza, in his journey through the n. circars, ( the madras lit. and scient. journ. vol. v. ) has described a formation with recent freshwater and marine shells, occurring at the distance of three or four miles from the present shore. dr. benza, in conversation with


( the madras lit. and scient. journ. vol. v. ) has described a formation with recent freshwater and marine shells, occurring at the distance of three or four miles from the present shore. dr. benza, in conversation with me, attributed their position to a rise of the land. dr. malcolmson, how - mauritius has certainly been upraised within the recent period, as i have stated in the chapter on fringing - reefs. the northern extremity of madagascar is described by capt. owen * as formed of madreporitic rock, as likewise are the shores and outlying islands along an immense space of eastern africa, from a little north of the equator for 900 miles southward. nothing can be more vague than the expression " madreporitic rock ; " but at the same time it is, i think, scarcely possible to look at the chart of the linear islets, which rise to a greater height than can be accounted for by the growth of coral, in front of the coast from the equator to 2° s., without feeling convinced that a line of fringing reefs has been elevated at a period so recent, that no great changes have since taken place on the surface of this part of the globe. some, also, of the higher islands of madreporitic rock on this coast, for instance pemba, have very singular forms, which seem to show the combined effect of the growth of coral round submerged banks, and their subsequent upheaval. dr. allan informs me that he never observed any elevated organic remains on the seychelles, which come under our fringed class. the nature of the formations round the shores of the red sea, as described by several authors, shows that the whole of this large area has been elevated within a very recent tertiary epoch. a part of this space in the appended map, is coloured blue, indicating the presence of barrier - reefs ; on which circumstance i shall presently make some remarks. ruppell † states that the tertiary formation, of which he has examined the organic remains, forms a fringe along the shores with a uniform height of from 30 and 40 feet, from the mouth of the gulf of suez to about lat. 26° ; but that south of 26°, the beds attain only the height of from 12 to 15 feet. this, however, can hardly be quite accurate ; although possibly there may be a decrease in the elevation of the shores in the middle parts of the red sea, for dr. malcolmson ( as he informs


the height of from 12 to 15 feet. this, however, can hardly be quite accurate ; although possibly there may be a decrease in the elevation of the shores in the middle parts of the red sea, for dr. malcolmson ( as he informs me ) collected from the cliffs of camaran island ( lat. 15° 30 ' s. ) shells and corals, apparently recent, at a ever, ( and there cannot be a higher authority on the geology of india ) informs me that he suspects that these beds may have been formed by the mere action of the waves and currents accumulating sediment. from analogy i should much incline to dr. benza ' s opinion. * owen ' s africa, vol. ii. p. 37 for madagascar ; and for s. africa, vol. i. pp. 412 and 426. lieut. boteler ' s narrative contains fuller particulars regarding the coral - rock, vol. i. p. 174., and vol. ii. pp. 41 and 54. see also ruschenberger ' s voyage round the world, vol. i. p. 60. † ruppell, reise in abyssinien, band i. s. 141. height between 30 and 40 feet ; and mr. salt ( travels in abyssinia ) describes a similar formation a little southward on the opposite shore at amphila. moreover, near the mouth of the gulf of suez, although on the coast opposite to that on which dr. ruppell says that the modern beds attain a height of only 30 to 40 feet, mr. burton * found a deposit replete with existing species of shells, at the height of 200 feet. in an admirable series of drawings by capt. moresby, i could see how continuously the cliff - bounded low plains of this formation extended with a nearly equable height, both on the eastern and western shores. the southern coast of arabia seem to have been subjected to the same elevatory movement, for dr. malcolmson found at sahar low cliffs containing shells and corals, apparently of recent species. the persian gulf abounds with coral reefs ; but as it is difficult to distinguish them from sand - banks in this shallow sea, i have coloured only some near the mouth ; towards the head of the gulf mr. ainsworth † says that the land is worn into terraces, and that the beds contain organic remains of existing forms. the west indian archipelago of " fringed " islands, alone remains to be mentioned : evidence


; towards the head of the gulf mr. ainsworth † says that the land is worn into terraces, and that the beds contain organic remains of existing forms. the west indian archipelago of " fringed " islands, alone remains to be mentioned : evidence of an elevation within a late tertiary epoch of nearly the whole of this great area, may be found in the works of almost all the naturalists who have visited it. i will give some of the principal references in a note. ‡ it is very remarkable, on reviewing these details, to observe in how many instances fringing - reefs round the shores, have coincided with the existence on the land of upraised organic * lyell ' s principles of geology, 5th edition, vol. iv. p. 25. † ainsworth ' s assyria and babylon, p. 217. ‡ on florida and the north shores of the gulf of mexico, rogers ' report to brit. assoc. vol. iii. p. 14. — on the shores of mexico, humboldt, polit. essay on new spain, vol. i. p. 62. ( i have also some corroborative facts with respect to the shores of mexico. ) — honduras and the antilles, lyell ' s principles, 5th ed. vol. iv. p. 22. — santa cruz and barbadoes, prof. hovey, silliman ' s journ vol. xxxv. p. 74. — st. domingo, courrojolles, jour. de phys. tom. liv. p. 106. — bahamas, united service journ. no. lxxi. pp. 218 and 224. — jamaica, de la beche geol. man. p. 142. — cuba, taylor in lond. and edin. phil. mag. vol. xi. p. 17. dr. daubeny also at a meeting of the geolog. soc. orally described some very modern beds lying on the n. w. parts of cuba. i might have added many other less important references. remains, which seem, from evidence more or less satisfactory, to belong to a late tertiary period. it may, however, be objected, that similar proofs of elevation, perhaps, occur on the coasts coloured blue in our map : but this certainly is not the case with the few following and doubtful exceptions. the entire area of the red sea appears to have been upraised within a modern period ; nevertheless i have


, perhaps, occur on the coasts coloured blue in our map : but this certainly is not the case with the few following and doubtful exceptions. the entire area of the red sea appears to have been upraised within a modern period ; nevertheless i have been compelled, ( though on unsatisfactory evidence, as given in the appendix ) to class the reefs in the middle part, as barrier - reefs ; should, however, the statements prove accurate of the less height of the tertiary beds in this middle part, compared with the northern and southern districts, we might well suspect that it had subsided subsequently to the general elevation by which the whole area has been upraised. several authors * have stated that they have observed shells and corals high up on the mountains of the society islands, — a group encircled by barrier - reefs, and, therefore, supposed to have subsided : at tahiti mr. stutchbury found on the apex of one of the highest mountains, between 5000 and 7000 feet above the level of the sea, " a distinct and regular stratum of semi - fossil coral. " at tahiti, however, other naturalists, as well as myself, have searched in vain at a low level near the coast, for upraised shells or masses of coral - reef, where if present they could hardly have been overlooked. from this fact, i concluded that probably the organic remains strewed high up on the surface of the land, had originally been embedded in the volcanic strata, and had subsequently been washed * ellis, in his polynesian researches, was the first to call attention to these remains, ( vol. i. p. 38. ) and the tradition of the natives concerning them. see also william ' s, nar. of miss. enterprize, p. 21 ; also tyerman and g. bennett, journ. of voyage, vol. i. p. 213 ; also mr. couthouy ' s remarks, p. 51 ; but his principal fact, namely, that there is a mass of upraised coral on the narrow peninsula of tiarubu, is from hearsay evidence ; also mr. stutchbury, west of england journ. no. 1. p. 54. there is a passage in von zach, corres. astronom. vol. x. p. 266., inferring an uprising at tahiti, from a footpath now used, which was formerly impassable ; but i particularly inquired from several native


von zach, corres. astronom. vol. x. p. 266., inferring an uprising at tahiti, from a footpath now used, which was formerly impassable ; but i particularly inquired from several native chiefs, whether they knew of any change of this kind, and they were unanimous in giving me an answer in the negative. out by the rain. i have since heard from the rev. w. ellis, that the remains which he met with, were ( as he believes, ) interstratified with an argillaceous tuff ; this likewise was the case with the shells observed by the rev. d. tyerman at huaheine. these remains have not been specifically examined ; they may, therefore, and especially the stratum observed by mr. stutchbury at an immense height, be contemporaneous with the first formation of the society islands, and be of any degree of antiquity : or they may have been deposited at some subsequent, but probably not very recent period of elevation ; for if the period had been recent, the entire surface of the coast - land of these islands, where the reefs are so extensive, would have been coated with upraised coral, which certainly is not the case. two of the harvey, or cook islands, namely, aitutaki and manouai, are encircled by reefs, which extend so far from the land, that i have coloured them blue, although with much hesitation, as the space within the reef is shallow, and the outline of the land is not abrupt. these two islands consist of coral - rock ; but i have no evidence of their recent elevation, besides, the improbability of mangaia, a fringed island in the same group, ( but distant 170 miles, ) having retained its nearly perfect atoll - like structure, during any immense lapse of time after its upheaval. the red sea, therefore, is the only area in which we have clear proofs of the recent elevation of a district, which, by our theory ( although the barrier - reefs are there not well characterized ), has lately subsided. but we have no reason to be surprised at oscillations of level of this kind having occasionally taken place. there can be scarcely any doubt that savage, aurora, * and mangaia islands, and several of the * aurora island is described by mr. couthouy ( remarks, p. 58 ) ; it lies 120 miles n. e. of tahiti


be scarcely any doubt that savage, aurora, * and mangaia islands, and several of the * aurora island is described by mr. couthouy ( remarks, p. 58 ) ; it lies 120 miles n. e. of tahiti ; it is not coloured in the appended map, because it does not appear to be fringed by living reefs. mr. couthouy describes its summit as " presenting a broad table - land which declines a few feet towards the centre, where we may suppose the lagoon to have been placed. " it is about 200 feet in height, and consists of reef - rock and conglomerate, with existing species of coral embeded in it. the island has been elevated at two successive periods ; the cliffs being islands in the friendly group, existed originally as atolls, and these have undoubtedly since been upraised to some height above the level of the sea ; so that by our theory, there has here, also, been an oscillation of level, — elevation having succeeded subsidence, instead of, as in the middle part of the red sea and at the harvey islands, subsidence having probably succeeded recent elevation. it is an interesting fact, that fais, which, from its composition, form, height, and situation at the western end of the caroline archipelago, one is strongly induced to believe existed before its upheaval as an atoll, lies exactly in the prolongation of the curved line of the mariana group, which we know to be a line of recent elevation. i may add, that elizabeth island, in the southern part of the low archipelago, which seems to have had the same kind of origin as fais, lies near pitcairn island, the only one in this part of the ocean which is high, and at the same time not surrounded by an encircling barrier - reef. on the absence of active volcanos in the areas of subsidence, and on their frequent presence in the areas of elevation. — before making some concluding remarks on the relations of the spaces coloured blue and red, it will be convenient to consider the position on our map of the volcanos historically known to have been in action. it is impossible not to be struck, first with the absence of volcanos in the great areas of subsidence tinted pale and dark blue, — namely, in the central parts of the indian ocean, in the china sea, in the sea between the barriers of australia and new caledonia, in the caroline, marshall,


show the effects of past and ancient eruptions. in these cases, it would appear as if the volcanos had come into action, and had become extinguished on the same spots, according as the elevating or subsiding movements prevailed. there are some other coasts on the map, where volcanos in a state of action concur with proofs of recent elevation, besides those coloured red from being fringed by coral - reefs. thus i hope to show in a future volume, that nearly the whole line of the west coast of south america, which forms the greatest volcanic chain in the world, from near the equator for a space of between 2000 and 3000 miles * see the note at p. 121, on the authorities for colouring the volcanos in the appended map. southward, has undergone an upward movement during a late geological period. the islands on the north - western shores of the pacific, which form the second greatest volcanic chain, are very imperfectly known ; but luzon, in the philippines, and the loo choo islands, have been recently elevated ; and at kamtschatka * there are extensive tertiary beds of modern date. evidence of the same nature, but not very satisfactory, may be detected in northern new zealand, where there are two volcanos. the co - existence in other parts of the world of active volcanos, with upraised beds of a modern tertiary origin, will occur to every geologist. † nevertheless, until it could be shown that volcanos were inactive or did not exist in subsiding areas, the conclusion that their distribution depended on the nature of the subterranean movements in progress, would have been hazardous. but now, viewing the appended map, it may, i think, be considered as almost established, that volcanos are often ( not necessarily always ) present in those areas where the subterranean motive power has lately forced, or is now forcing outwards the crust of the earth, but that they are invariably absent in those, where the surface has lately subsided or is still subsiding. ‡ on the relations of the areas of subsidence and elevation. — the immense surfaces on the map, which, both by our theory and by the plain evidence of upraised marine remains, have undergone a change of level either downwards or upwards during a late period, is a most remarkable fact. the exis - * at sedanka, in lat. 58° n. ( von buch ' s descrip. des isles canaries, p. 455.


or upwards during a late period, is a most remarkable fact. the exis - * at sedanka, in lat. 58° n. ( von buch ' s descrip. des isles canaries, p. 455. ) in a forthcoming part, i shall give the evidence referred to with respect to the elevation of new zealand. † during the subterranean disturbances which took place in chile in 1835, i have shown ( geolog. trans. 2nd ser. vol. v. p. 606. ) that at the same moment that a large district was upraised, volcanic matter burst forth at widely - separated points, through both new and old vents. ‡ we may infer from this rule, that in any old deposit, which contains interstratified beds of erupted matter, there was at the period, and in the area of its formation, a tendency to an upward movement in the earth ' s surface, and certainly no movement of subsidence. tence of continents shows that the areas have been immense, which at some period have been upraised : in south america we may feel sure, and on the north - western shores of the indian ocean we may suspect, that this rising is either now actually in progress, or has taken place quite recently. by our theory, we may conclude that the areas are likewise immense which have lately subsided, or, judging from the earthquakes occasionally felt and from other appearances, are now subsiding. the smallness of the scale of our map should not be overlooked : each of the squares on it contains ( not allowing for the curvature of the earth ) 810, 000 square miles. look at the space of ocean from near the southern end of the low archipelago to the northern end of the marshall archipelago, — a length of 4500 miles, in which, as far as is known, every island, excepting aurora which lies just without the low archipelago, is atoll - formed. the eastern and western boundaries of our map are continents, and they are rising areas : the central spaces of the great indian and pacific oceans, are mostly subsiding ; between them, north of australia, lies the most broken land on the globe, and there the rising parts are surrounded and penetrated by areas of subsidence, * so that the prevailing movements now in progress, seem to accord with the actual states of surface of the great divisions of the world. the blue spaces on the map are nearly all elongated ; but it does not necessarily follow from this, ( a