Dp aig Hot 
3 i or tens x - 
we ~* 
e) 
and Number of Animals in Geological Times. 285 
certain results as general which would require various quali- 
fications to be true. In comparing fossils of one and the 
same or of different geological formations, it is in reality 
not enough to ascertain their true geological horizon, which 
we may call the chronological element of the inquiry ; 
it is equally important that the differences or resemblances 
arising from the geographical distribution over the wide 
expanse of the whole surface of the globe, which we may 
call the topographic element of the question, should be 
also considered, for it is already known that within certain 
limits the same differences and resemblances which are ob- 
served at present between the animals inhabiting different 
parts of the globe existed already in former geological periods. 
We must, therefore, become acquainted with the general 
biological character of the epoch, as well as with the locale 
faune of each period. The tertiary faune of New Holland 
and the Brazils, for instance, resemble more closely the living 
faune of those parts of the world than they resemble one 
another. Our lists of fossils teem with chronological errors 
of the worst kind, arising partly from false identifications of 
strata which in reality belong to different periods, but the 
fossils of which are thus represented as having inhabited our 
globe simultaneously, when in reality they may have been 
separated by long periods of time, and existed upon the earth 
under very different physical conditions. This chronological 
confusion is further increased by the too extensive limits 
frequently assigned by geologists to the successive groups 
of rocks forming the crust of our globe. For instance, when 
the cretaceous or the oolitic formations are considered re- 
spectively as indivisible natural groups, and the fossils of all 
their subdivisions are enumerated in one single list as the 
inhabitants of a long period, an infinitude of anachronisms 
are presented to the mind, which no special mention of loca- 
lities can rectify ; and until the fossils of each of the natural 
subdivisions of these formations shall have been grouped to- 
gether and compared carefully, as I have attempted to do 
in my Monographs of the T rigonice and of the Mye of Swit- 
zerland and the adjoining countries, or as Al. D’Orbigny has 
done upon a much larger scale in his Paléontologie Fran- 
