Miscellaneous. 379 



each other much as they now differ : in fact (according to Adolphe 

 Brongniart, whose statements we here condense*), the inhabitants 

 of these different regions appear for the most part to have acquired, 

 before the close of the Tertiary period, the characters which essen- 

 tially distinguish their existing faunas. The eastern continent had 

 then, as now, its great Pachyderms, Elephants, Rhinoceros, and 

 Hippopotamus ; South America its Armadillos, Sloths, and Ant- 

 eaters ; Australia a crowd of Marsupials ; and the very strange birds 

 of New Zealand had predecessors of similar strangeness. Everywhere 

 the same geographical distribution as now, with a difference in the 

 particular area, as respects the northern portion of the continents, 

 answering to a warmer climate then than ours, such as allowed spe- 

 cies of Hippopotamus, Rhinoceros, and Elephant to range even to 

 the regions now inhabited by the Rein-deer and the Musk-ox, and 

 with the. serious disturbing intervention of the glacial period within 

 a comparatively recent time. Let it be noted also, that those Tertiary 

 species which have continued with little change down to our days 

 are the marine animals of the lower grades, especially Mollusca. 

 Their low organization, moderate sensibility, and the simple condi- 

 tions of an existence in a medium like the ocean, not subject to great 

 variation, and incapable of sudden change, may well account for their 

 continuance ; while, on the other hand, the more intense, however 

 gradual, climatic vicissitudes on land, which have driven all tropical 

 and subtropical forms out of the higher latitudes and assigned to 

 them their actual limits, would be almost sure to extinguish such 

 huge and unwieldy animals as Mastodons, Mammoths, and the like, 

 whose power of enduring altered circumstances must have been small. 



This general replacement of the Tertiary species of a country by 

 others so much like them is a noteworthy fact. The hypothesis of 

 the independent creation of all species, irrespective of their antece- 

 dents, leaves this fact just as mysterious as is creation itself; that of 

 derivation undertakes to account for it. Whether it satisfactorily 

 does so or not, it must be allowed that the facts well accord with that 

 assumption. 



The same may be said of another conclusion, namely, that the 

 geological succession of animals and plants appears to correspond in 

 a general way with their relative standing or rank in a natural system 

 of classification. It seems clear that though no one of the grand 

 types of the animal kingdom can be traced back further than the 

 rest, yet the lower classes long preceded the higher ; that there has 

 been on the whole a steady progression within each class and order ; 

 and that the highest plants and animals have appeared only in rela- 

 tively modern times. It is only, however, in a broad sense that this 

 generalization is now thought to hold good. It encounters many 

 apparent exceptions, and sundry real ones. So far as the rule holds, 

 all is as it should be upon a hypothesis of derivation. 



The rule has its exceptions; but, curiously enough, the most 

 striking class of exceptions, if such they be, seems to us even more 



* In Comptes Rendus de l'Acad. des Sciences, Fe'vr. 2, 1857. 



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