Se es eee Tor ey 
Oe ees 
ES Dene et Oe an ie 
ners 
Miscellaneous. 379 
each other much as they now differ : in fact (aceording 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 aceord 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 
spearen exceptions, and sundry real ones. So far as the rule holds, - 
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, Févr. 2, 1857. 
25* 
