and Number of Animals in Geological Times. 275 
we shall find, in every instance, similar results. The tertiary 
fossils of Bordeaux, though less numerous in species than 
those of the eocene in the vicinity of Paris, will compare 
with any local fauna of the present period as favourably for 
variety and number of species as those of the lower tertiaries. 
This may be said, with the same certainty, of the tertiary 
shells of the Sub-Apennine Hills, or of those of the English 
Crag, of which we now possess a very complete list. : 
If from the tertiary periods we pass down to the cretaceous, 
do we not find in the deposits of Mestricht, or in those of 
the age of the white chalk, a number and variety of shells as 
great as that which may be found on any shore or in any 
circumscribed marine basin of an extent at all comparable 
with that of the cretraeous beds within similar limits? Do 
we not find in the lower cretaceous strata, such as the green 
sand or the Neocomien, other assemblages of the remains of 
Mollusks, which, in number and variety, are not inferior to 
those of the white chalk? The oolitic series, again, will 
stand a similar comparison quite as well. We need not 
even take the whole group of those deposits, but consider 
each subdivision of the Jurassic period by itself, and still we 
find in every one local faune of Mollusks, assuming of 
course a different character from those of the cretaceous or 
tertiary, but nevertheless sufficiently diversified to admit of 
an estimate as advantageous with respect to the points un- 
der consideration, and to the local faunz of the present day, 
as to the cretaceous assemblages of fossils, or those of the 
tertiary period. Of course, in accordance with the peculiar 
character of the age, different families prevail in these differ- 
ent periods; the Cephalopoda are extremely numerous and 
surprisingly diversified during the cretaceous and oolitic 
periods ; while they dwindle down to a few representatives 
in the tertiaries, and so with other families. The shells 
found in the deposits of the new red sandstone period, of . 
the coal period, and of the still earlier ages, are perhaps less 
numerous on the whole, though they can hardly be said to 
be less diversified ; for the extinct forms which occur among 
them are quite an equivalent to the variety of their families 
which have lived during more recent periods ; and the daily 
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