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Show 300 GEOLOGICAL SUCCESSION. [CHAP. X. to leave no modified offspring on the face of th~ earth. But the utter extinction of a whole group of speCJes may often be a very slow process, from the .survival. of a. few descendants lingering in protected and Isolated Situations. When a gr~up bas once wholly disappeared, it does not reappear ; for the link of generation has peen brok~n. -we can understand how the spreading of the dominant forrns of life, which are those that oftenest vary, will in the long run tend to people the world with allied, but modified, descendants ; and these will generally succeed in taking the places of those groups of species which are their inferiors in the struggle for existence. Hence, after long intervals of time, the productions of the world will appear to have changed simultaneously. We can understand h0w it is that all the forms of life, ancient and recent, make together one grand systmn ; for all are connected by generation. We can understand, from the continued tendency to divergence of character, why the more ancient a form is, the more it generally differs from those now living. Why ancient and extinct forms often tend to fill up gaps between existing forms, sometimes blending two groups previously classed as distinct into one ; but more commonly only bringing them a little closer together. The more ancient a form is, the more often, apparently, it displays characters in some degree intermediate between groups now distinct; for the more ancient a forrn is, the more nearly it will be related to, and consequently resemble, the common progenitor of groups, since become widely divergent. Extinct forms are seldom directly intermediate between existing forms; but are intermediate only by a long and circuitous course through many extinct and very different for1ns. We can clearly see why the organic remains of closely consecutive formations are more closely allied to each other, than are those of remote formations ; for the forms are more closely linked together by generation : we can clearly see why the remains of an intermediate formation are intermediate in character. . The inhabitants of each successive period in the world's h1story have beaten their predecessors in the race for life, OHAP. X.] SUMMARY. 301 and are, in so far, higher in the sc 1 f J' a e o nature . and th• may account 10r that vague yet ill-defin d ? IS by many palreontologists, that OrO'anisat~ senti~hent, felt has progressed. If it should h5 Ion on e whole ancient animals resemble to a cer::i~~e~ b: tl:roved that of more recent animals f th x en e embryos intelligible. The succe~ion ~f:~e classt the fact will be within the same areas durinO' theel s:me y~es .of struc~ure ceases to be mysterious and is . a ei geo ogi?al periods heritance. ' simp Y explained by in-liev~ i~t~n ~:,ea~~o~~~~~ :~cl:a~t\~ as imfdrfehct as I be-ord cannot be proved to be h e asser e t at the reoobjections to the theor f muc more p~rfect, the main diminished or a· y oonatural selection are greatly Isappear. n the th h d ll . laws of palreontology plainly procl~i;:r a; ' a the ch1ef that species have been produced by 'da;s I seems to. me, old forms havin been or mary generation: !~:d ~s~i~l~~~~~~!i{;h~~::a~~:Eti~!; s~ffiP:~ti~~ ' ' |