MOST IMPORTANT TO GEOLOGY. 267 
at length been undertaken by an individual, to 
whose hands Cuvier at once consigned the 
materials he had himself collected for this 
important work. The able researches of Pro- 
fessor Agassiz have already extended the num- 
ber of fossil Fishes to two hundred genera, and 
more than eight hundred and fifty species.* 
The results of his enquiry throw a new and most 
important light on the state of the earth, during 
each of the great periods into which its past 
history has been divided. The study of fossil 
Ichthyology is therefore of peculiar importance 
to the geologist, as it enables him to follow an 
entire Class of animals, of so high a Division as 
the vertebrate, through the whole series of geo- 
logical formations ; and to institute comparisons 
between their various conditions during succes- 
sive Periods of the earth's formation, such as 
Cuvier could carry only to a much more limited 
extent in the classes of Reptiles, Birds, and 
Mammifers, for want of adequate materials. 
ment of these Fishes has been more or less defective, from an 
endeavour to arrange them under existing genera and families. 
The imperfection of his own, and of all preceding classifications 
of Fishes, is admitted by Cuvier ; and one great proof of this 
imperfection is that they have led to no general results, either in 
Natural History, Physiology, or Geology. 
* No existing genus is found among the fossil Fishes of any 
stratum older than the Chalk formation. In the inferior chalk 
there is one living genus, Fistularia ; in the true chalk, five ; and 
in the Tertiary strata of M. Bolca, thirty-nine living genera, and 
thirty-eight which are extinct. — Agassiz. 
