286 L. Agassiz on the Primitive Diversity 
goise, no correct ideas can be formed respecting the succes- 
sion of animals and plants characteristic of these long suc- 
cessive periods. I do not believe there is a single paleonto- 
logist, whose opinion is worth having, who can suppose, at 
this day, that any of the animals, the remains of which are 
buried in the lias, lived simultaneously with those of the in- 
ferior oolite, or these with those of the Oxford clay, or these 
with those of the upper division of the so-called oolitic for- 
mation. ‘The same may be said of the different natural sub- 
divisions of the cretaceous formation, and of the subdivisions 
introduced of late among the paleozoic rocks, by Sir Rode- 
rick Murchison and Professor Sedgwick, and in America 
by Professor J. Hall. : 
But even after this separation of the fossils, the synchron- 
ism of which may be fully established, our task is only fairly 
laid open, for then must begin the zoological identification of 
all the species, which has to be correct in every respect before 
general conclusions can be drawn from it. 
In the first place, the specific identity of organic remains is 
not so easily ascertained as many geologists would seem to 
suppose, if we judge from their statements ; but unless the 
validity of a species is sanctioned by a practised zoologist, it 
cannot be taken as a basis for sound generalizations in re- 
ference to questions of a purely zoological character. The 
number of false identifications which have been accumulated 
in geological works is truly frightful. It would be, however, 
very unjust to accuse geologists in general of inaccuraey for 
this; the fault is mostly to be traced to other. parties from 
which the names were obtained. It should only be understood 
that the materials thus accumulated are no longer fit to be 
used for the discussion of the questions which have been 
raised with the modern progress of geology, and that a tho- 
rough revision of al/ the identifications made in former years 
is imperatively demanded by the modern progress of paleon- 
tology. It would be, however, sometimes amusing, were it 
not actually distressing, to see the manner in which some 
geologists deal with fossils, considering them simply as the 
characteristics of certain rocks, and hardly yet dreaming that 
there may be such a thing as a special zoology of the differ- 
