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Show 286 GEOLOGICAL SUCCESSION, [CB.A.P. X. life throughout the world, accords well with ~he princiJ.?le of new species having be~n formed by dom:nant species spreading widely and varying_; the ne'Y" speCl~S th~s produced being themselves dominant owing to Inhentanc~, and to having already had some adv.antage o.ver thmr parents or over o.ther species; ~hese again spreading,. var~ing and produCing new specws. The forms whwh. a1e be~ten and which yield their plac~s t~ the new and VlC~Orious forms will generally be alhed In groups, from Inheriting so~e inferiority in common ; and therefore as new and improved groups spread throughout the world, old groups will disappear froin :the world ; and the succession of forms in both ways will everywhere tend to cor-respond. · . . . There is one other remark connected with this subJect worth making. I have given iny reasons for believing that all our greater fossiliferous formations were ~eposited during periods of subsidence; and that blank Intervals of vast duration occurred during the periods when the bed of the sea was either stationary or rising, and likewise 'vhen sediment was not thrown down quickly enough to ~bed and preserve organic remains. During these long and blank intervals I suppose that the inhabitants of each region underwent a considerable amount of modification and extinction, and that there was much migration fror_n other parts of the world. As we have reason to be~ lieve that large areas are affected by the same movement, it is probable that strictly contemporaneous formations have often been accumulated over very wide spaces in the same quarter of the world ; but we are far from having a.ny right to conclude that this has invariably been the case, and that large areas have invariably been affected by the same movements. When two formations have been deposited in two regions during nearly, but not exactly the same period, we should find in both, fro;m the causes explained in the foregoing paragraphs, the same general succession in the forms of life; but the species would not exactly correspond; for there will have been a little n::ore time in the one region than in the other for modificatwn, extinction, and immigration. CHAP, X.] THROUGHOUT THE WORLD. 28'7 I suspect that cases of this nature have occu. d . Europe. Mr. Prestwich, in his admirable Me · Ire hin eocene d eposi· ts of E ngland and France is abml ot nsd o n t e 1 1 11 1. ' e o raw a c ose genera ~ara e Ism between the successive stages in t·h eE t wo countries; but when he compares cert · t In ng1 a nd W·i t h t h ose I.n France although h ainf i sd a ge· s b th · . ' e n s In o a. curious accordance In the nuinbers of the s ecies b~longing to the same g~nera, yet the species them~el ves differ In a manner very difficult to account .['or 'd · th ' 't f h 11 , COnSI erinO' e proximi y o . t e two areas,-unless, indeed, it b~ a~s~med that an Isthmus separated two seas inhabited b ~1st~nct, but co~temporaneous, faunas. Lyell has mad~ s~m1lar observations on some of the later tertiar formatiOns. Barrande, also, shows that there is a y t 'k · ~eneral. parallelism ~n the successive Silurian dep~~ts~f ~h.emia and Scan~1navia; _nevertheless he finds a sur-. p/.' risingt' amo· untht of drffe·r ence In the species · If th e severa1 10rma Ions In ese r_eg1ons have not been deposited durin the. same e_xact :per1ods,-a formation in one region ofte~ ?Oriespondi_ng With a blank Interval in the other -and if In ~oth regions the species have gone on slowly ~hanging dur-~ng the accumulation of the several formations and during the long intervals of time between them . in th · s case, the ~everal formations in the two regions dould be arrang~d In the same order, in accordance with the eneral succession of the form of Hfe, and the order wouldgfalsely app~dr to be strwtly pa~allel ; nevertheless the species wou ·?-ot all be the ~arne In the apparently corresponding stages m the two regions. Plf!' the Affinities of extinct Species to each other and tf l~v;.ng forms:-. Let us ?J-OW look to the mutual a:ffi~ities ~ .ex met and hvmg spemes. They all fall into one rand a~r.al1 system; and this fact is at once explained !n the prmmp e of descent. The more ancient any form is . the moB, ahl a general rule, it differs from living forms But :ftheu~ a;u~ lo~g. ago remarked, all fossils can be ·classed extin r :£ s exflS~Ing groups, or between them. That the tw c ~r~s 0 hfe help to :fill up the wide intervals be-een eXIsting genera, families, and orders, ~annot be dis- |
