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Show 268 IMPERFEOTION OF THE [ODAP. IX. minutes on some one barren point i~ Australi~, and then to discuss the number and range of 1ts productions. On the sudden appearance of groups oi Alli~d Species in the lowest. known jossi_life;ous strata.-There 1s another and allied difficulty, whiCh 1s much graver. I allude to the manner in which numbers of species of the same group, suddenly appear in the lowest known fossiliferous rocks. Most of the arguments which have convinced me that all the existing species of the same group have descended from one progenitor, apply with nearly equal force to the earliest known species. For instance, I cannot doubt that all the Silurian trilobites have descended from some one crustacean, which must have lived long before the Silurian age, and which probably differed greatly from any known anin1al. Some of the most ancient Siludan animals, as the N au til us, Lingula, &c., do not differ much from living species; and it cannot on my theory be supposed, that these old species were the progenitors of all the species of the orders to which they belong, for they do not present characters in any- degree intermediate between them. If, moreover, they had been the progenitors of these orders, they would almost certainly have been long ago supplanted and exterminted by their numerous and improved descendants. Consequently, if my theory be true, it is indisputable that before the lowest Silurian stratum was deposited, long periods elapsed, as long a~, or probably far longer than, the whole interval fron1 the Silurian age to the present day ; and that during these vast, yet quite unknown, periods of time, the world swarmed with living crea-tures. · To the question why we do not find records of these vast primordial periods, I can give no satisfactory answer. Several of the most eminent geologists, with Sir R. Murchison at their head, are convinced that we see in the organic remains of the lowest Silurian stratum the dawn of life on this planet. Other highly competent judges, as Lyell and the late E. Forbes, dispute this conclusion. We should not forget that only a small portion of the world is 0HAP. IX.] GEOLOGIO.AL UEOORD. k . h 269 nown Wit accuracy M B another and lower stage to the s~ra~de, has lately added with new and pecuHar s ec · I Urian systeJ?, aboundin~ detected in the Longmy~d I~sd ~aces of hfe have been called primordial zone. The er: eneath Barrande's soules and bituminous matter .P sence of phosphatic nodrocks, probably indicates th I£ some of .the lowest azoic these periods. But the diffl }~mer existence of life at absence of vast piles of fos .1?Z Y of understanding the t~eory no doubt were some~h:;ous strata, which on my Silurian epoch, is very great If :~cumulated before the had been wholly worn awa ·b d ese :nost ancient beds by metamorphic action weyouy h:~u1ation, or obliterated nants of the formationd next g ~. nd only small remthese ought to be ver ener suc?ee Ing them in age, and dition. But the desc~ifftionsall1 ~~ a metamorphosed conSilurian deposits over imme w ~c 1 ;ve now possess of the in North Ainerica, do not su nse erntoi:ies in Russia and a formation is the more it lpport ~he VIew, that the older denudation an'd metamotph .las su ered the extremity of Th Ism. e case at present must . . may be truly urged as a valid a:.emain Inex~licable ; and here entertained. To show tl t &~ment agalnst the views some explanation, I will O'iv~a h may h~reafter receive From the nature of the or ~ni t e ~ollowu:g hypothesis. pear to have inhabited g £ c remains, which do not ap-formations of Europe andp~f t~un¥J ~epths, in the several the amount of sediment . ~ ni~ed States ; and from formations are composed miles In ~hickness, of which the last larg-e islands or tradt wef ~ay Infer that from first to ~as derived, occurred in :h~ a?~ whence the sediment Ing continents of Europe dn1l.: bourhood of the existdo not know what was the ~~at orth. A~erica. But we ;htwUee~ the successive formati~ of .thnhgshin the intervals e mted States durin h ~s' w et er Europe and land, or as a submari g t ese Intervals existed as dr ment was not deposit~~ surface ?ear land, on which seal and unfa~homable sea. ' or again as the bed of an open Looking to the e . t' . x~s Ing oceans, which are thn .e e as |