324 L. Agassiz on Animals in Geological Times. 
ent types within definite regions, and their common circumserip- 
tion within natural zoological provinces. This study would be 
particularly important with reference to the comparison. of the 
local faunee of former geological periods with those of the pres- 
ent creation. But since the latter even are comparatively little 
known, we must be’satisfied to wait for the time when thorough 
comparisons shall be possible between the local faune of each and 
all geological periods inter se, and with those of other periods. 
identity of the species, their generic affinities and their zoological 
classification should be equally tested. : 
and profusely scattered upon the whole globe, at all times and du- 
ring all geological periods, as it is now. No coral reef in th 
Pacific contains a larger amount of organic debris than some 
the limestone deposits of the tertiary, of the cretaceous, or of the 
oolitic, nay even of the paleozoic periods, and the whole veget@ 
e€ carpet covering the present surface of the globe, even if we 
were to consider only the most luxurious vegetation of the trop 
ics, and leave entirely out of consideration the whole expanse of 
the ocean, as well as those tracks of land where under less favor- 
able circumstances the growth of plants is more reduced, woul 
not form one single seam of workable coal to be compared to the 
many thick beds contained in the rocks of the Carboniferous 
period alone. 
