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Show 282 GEOLOGICAL SUCCESSION, [ORAP. X. obscured. \Vhenever we can precisely say why this sp~cies is more abundant in individuals than. that ~ why _this species and not another . can be naturahs~d u1 a give~ connt ry ., then , and not till then ' we m. ay J· Ustlyf tfhee · l sur-prise why we cannot account fo: .th~ extmction o IS par-ticular species or group of spemes. On the Forms of Life changing alrnost simulta_neo~s?y throughout tiM World.-Scarcely any palreontologiCal discovery is more striking than the fact, that the forms of life change almost simultaneously throughout the world. Thus our European Chalk formation can be recog~ised in many distant parts of the world, under ~he most dia:erent climates, where not a fragment of the mi~era~ chalk Its~lf can be found; namely, in North America, In equatorial South America in Tierra del Fuego, at the Cape of Good Hope, and in the peninsu~a of. India .. For at these distant points, the organic remams In certain beds present an unmistakeable degree of resemblance to those of the Chalk. It is not that the same species are met with ; for in some cases not one species is identically the same, but they belong to th~ same faJ?i~ies, genera, and sections of genera and sometimes are similarly characterised in such trifli~g points as mere superficial sculpture. . Moreover other forms, which are not found in the Chalk of Europe, but which occur in the formations. either ab?ve or below are similarly absent at these distant pmnts of the w~rld. In the several succesBive palreozoic formations of Russia, Western Europe and North America, a similar parallelism in the forms of life has been observed by several authors : so it is, according to Lyell, with the several European and North American tertiary deposits. Even if the· few fossil species which are common to the Old and New Worlds be kept wholly out of view, the general parallelism in the successive form~ of life, in. the stages of the widely separated palreozoic and tert~ary periods, would still be manifest, and the several formatwns_ could be easily correlated. . . These observations, however, relate to the manne In· habitants of distant parts of the world: we have not suffi- CHAP. X.] THROUGHOUT '.rHE WORLD. , 283 . ' cient data to judge whether the productions of the land and of fresh water change at distant points in-the same parallel m~nner. We maY: doubt whether they have thus changed : If the Megathenum, Mylodon Macrauchenia a~d Toxodon. had bee.n b~ought to Europ~ frmn La Plata: without any Infonnation In regard to their o-eological position, no one would have suspected that t~ey had coexisted with still Hving sea-shells; but as these anomalo~s m9nsters coexisted with the Mastodon and Horse it mio-ht at least have been inferred that they had lived d~ring gne of the later tertiary stages. When the marine forms of life are spoken of as ha vinochanged simultaneously throughout the world it must not · be supposed that this expression relates to th~ same thousandth ~r hundre~-thousandth year, or even that it has a very stnct geological sense ; for if all the marine animals which. live. at the presen~ day in Europe, and all those that hved In Europe ~unng the pleistocene period (an ~normously remote .penod as measured by years, includIng the wh~l~ gla.mal epoch), we~e to be compared with those no.w hving In South America or in Australia, the most skilful r~at~ralist woul~ hardly. be able to say whether the existing or the plmstocene Inhabitants of Europe resembled most closely those of the southern hemisph~ re. So, again_, ~everal highly competent observers beheve that the existing productions of the United States are .more cl~sely related to those which lived in Europe during certain later tertiary stages, than to those which ?OW hve here; and if this be so, it is evident that fossiliferous beds deposited at the present day on the shores of N.orth America would hereafter be liable to be classed ~th somewhat older European beds. Nevertheless, lookIng to a remotely future epoch, there can, I think be little doubt that all the more modern marine formatio~s namely, the upper pliocene, the pleistocene and strictly :z'nodern beds, of Eu_r~pe, N or~h and ~ou~h America, and Australia, from cont~In~ng. fossil remains In some degree allied, and from not Includ~ng those forms which are only found in the ?lder underlying deposits, would be correctly ranked as Simultaneous in a geological sense. |