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Show [CHAP. X. GEOLOGICAL SUCCESSION. 292 b tween the pre-d. t ·n character, e doubtedly is interme. Ia e ~ I need give ?n1 y one ceding and succeeding fauna~. which the fossils of the instance, namely, the mani:rsi~tem was firs~ discove~·ed, Devonian system, ~hen th alJontologists as Inter~ediate were at once recognisei by ~f the overlying carbonif~rous, in character betw~en ~ ose t But each fauna IS not and underlying Sih:nan syds. etme. as unequal intervals of necessari. ly exac tly 1nterme c1oan s,e cutive formati·o ns. time have elapsed. be~ween the truth of the statement, ~hat It is no real obJection to h le is nearly intermediate the fauna of each perit a~:c:di~g and succeeding faun~s, in character between t e p tions to the rule. For Inthat certain genera offer txh?n.ts when arranged by Dr. stance, ro.astodons ~nd fi. er according to their :n:utual affiFalconer Ill two serie~~ rst their periods of existence, do nities and t~len accor Ing to The species extreme in charnot accord In arrangemen . th most recent . nor are those acter are not the ol~est, ~r ~aracter inter~diate in age. which are intermedia~e In ~ . this ~nd other such cases, But supposing fof a~ Ifl~~~n a~;earance and disappear~nce that the record o t e £ t have no reason to beheve of the speCi·e S was . pe1r ec ' wdue ced ne·c essar.i ly end ur.e £o r that forms. succssiv~ y l!ti~e. a very ancient fonn Inight corresponding lengt so n er 'than a form elsewhere sub~ occasionally last much lo g ll ·n the case of terrestrial sequently lw?duce?! especla rltea districts. To compare producti.ons m_h~bitin~. sift~e principal living and extinct small things wit g;ea . . . were arranged as well as they races of th~ dom~stic p~~on this arrangement would .not could be In ser~al affi older in time of their productiOn, clo~elJ: accord ;v~t~l the der of th~ir disappearanc~ ; for the and still less wit le or r . and many vanetles be-parent rock-pigeo;t now d"~~~ carrier have become extween the rock~pigeon. an xtreroe in the important tinct. and carriers which karhe e ··gi'nated earlier than chara'c ter of 1e ng th of bea ave on . d f 1 . h. h are at the opposite en o short-beaked turob ers, w IC the series in this same r~spe~t. t tement that the organic Closely connec~ed withd~ te sf~rmatio~ are in some de· remains from an lnterme Ia e ORAl'. X.] AFFINITIES OF EXTINCT SPECIES. 293 gree intermediate in character, is the fact, insisted on by an palreontologists, that fossils from two consecutive formations are far n1ore closely related to each other, than are the fossils from two remote formations. Pictet gives as a well-known instance, the general resemblance of the organic remains from the several stages of the chalk formation, though the species are distinct in each stage. This fact alone, from its generality, seems to have shaken Professor Pictet in his firm belief in the immutability of species. He who is acquainted with the distribution of existin~ species over the globe, will not attempt to account for the close resemblance of the distinct species in closely consecutive formations, by tho physical conditions of the ancient areas having remained nearly the saine. Let it be remembered that the forms of life, at least those inhabiting the sea, have changed almost simultaneously throughout the world, and therefore under the most different chmates and conditions. Consider the prodigious vicissitudes of climate during the pleistocene period, which includes the whole glacial period, and note how· little the specific forms of the inhabitants of the sea have been affected. On the theory of descent, the full meaning of the fact of fossil remains from closely consecutive formations, though ranked as distinct species, being closely related, is obvious. As the accumulation of each formation has often been interrupted, and as long blank intervals have intervened between successive formations, we ought not to expect to find, as I attempted to show in the last chapter, in any one or two formations, all the intermediate varieties between the species which appeared at the commencement and close of these periods ; but we ought to find after intervals, very long as measured by years, but only moderately long as measured geologically, closely allied forms, or, as they have been called by some authors, representative species ; and these we assuredly do find. We ~nd, in short, such evidence of the slow and scarcely sen4 Sible mutation of specific forms, as we have a just right to expect to find. On the state of .Development of Ancient Forms.There has been much discussion whether recent forms are |