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Show 290 IMPERirECTION OF THE CHAP. IX. and great changes in the mineralogical composition of consecutive formations, generally implying great changes in the geography of the surrounding lands, whence the sediment has been derived, accords with the belief of vast intervals of time having elapsed between each for-mation. But we can, I think, see why the geological forma-tions of each region are almost invariably intermittent; that is, have not followed each other in close sequence. Scarcely any fact struck me more when examining many hundred miles of the South American coasts, which have been upraised several hundred feet within the recent period, than the absence of any recent deposits sufficiently extensive to last for even a short geological period. Along the whole west coast, which is inhabited by a peculiar marine fauna, tertiary beds are so scantily developed, that no record of several successive and peculiar marine faunas will probably be preserved to a distant age. A little reflection will explain why along the rising coast of the western side of South America, no extensive formations with recent or tertiary remains can anywhere be found, though the supply of sediment must for ages have been great, from . the enormous degradation of the coast-rocks and from muddy streams entering the sea. The explanation, no doubt, is, that the littoral and sub-littoral deposits are continually worn away, as soon as they are brought up by the slow and gradual rising of the land within the grinding action ofthe coast-waves. We may, I think~ safely conclude that sediment must be accumulated in extremely thick, solid, or extensive masses, in order to withstand the incessant action of the waves, when first upraised and during subsequent oscillations of level. Such thick and extensive accumulations of sediment may be formed in two ways ; either, C. HAP. IX. GEOLOGICAL RECORD . 291 In profound depths of the sea . h. from the researches of E F b' In w wh case, judging the bottom will be inhab .. t ~rb es, we may conclude that and the mass when uprai~e~ wfu ex~emely few_ animals, record of the forms of life hi h tghive a ~ost Imperfect t w c en existed · d' men may be accumulated to an . ' or, se l-over a shallow bottom if . t t. y thickness and extent In this latter case a~ lo I con ~nue slowly to subside. and supply of sedimentn~e:~l he rate of subsidence the sea will remain shallo y balance each other, thus a fossiliferous forma~o~~~a~ourable for life, and raised, to resist any amount of ~ eno~g_h, when up-formed. egradation, may be I am convinced that all . which are rich in £ il hour ancient formations, during subsidence· s~~~e s, u~~·e hi thus been formed this subject in 1845 I h p IS ng my views on Geology and h ' ave watched the progress of after auihor, in :;:at:;:t:rrised to note how author has come to the con I . s or t~at great formation, during subsidence. Ic :Ion that It was accumulated tertiary formation h ay add, that the only ancient which has been bul~ t e west coast_ of South America, as it has as yet suffe~e~n~ugh to. resls~ such degradation distant eolo . ' ut which will hardly last to a downw!d ofc;h~t~:' 7~ certainly deposite~ during a derable thickness. o evel, and thus gained consi-ha All dgeological fact.s tell us plainly that each s un ergone nume rous · 1 · · area apparently th . . . s ow osCillations of level, and Consequent! e£s e osC.i llation. s h.a v e au£(!e ct e d W·i de spaces. thick and e~t or~ations rich In fossils and sufficiently may have bee:~~~::e~o resist . subsequent d~gradation, of subsidence b t nl over wide spaces dunng periods was sufficient' to ~ o th where the supply of sediment eep e sea shallow and to embed and 0 2 |