4 [Senate 
and making such a one as I considered was demanded, even at the 
risk of being charged with unworthy motives in prolonging the work. 
Accordingly, I commenced making very full collections of fossils, 
which I was obliged either to purchase or have made at my own ex- 
pense, for I was allowed no assistant, and I could give very little 
time to the actual collection of specimens myself, having the neces- 
sary investigations and comparison of species to make, the drawing 
and engraving to superintend, and the descriptions to write and print. 
The investigation of fossils, particularly of the older rocks, is at- 
tended with many difficulties which are not encountered in the more 
recent formations, or in the existing objects of a similar character. 
In the first place, the collections are more difficult to be made, the 
specimens are often embedded in solid rock, from which they require 
to be separated with much labor and great care. Often we have 
only one side exposed at best, the specimens have suffered pressure 
and distortion; sometimes Vv^e have only casts of the interior of the 
specimen, while tlie organized portion has disappeared. Conclusions 
have often to be based upon fragments when perfect specimens can- 
not be obtained. These fossils of our rocks, being farthest removed 
in time, and most unlike existing creations, the latter afford little 
assistance in comparisons made between the two. More than four- 
fifths of all the species described from the rocks of New-York are 
new, having never been described in any published work. This does 
not lessen the labor of comparison with described species, and imposes 
a heavier task in the determination and description. 
When I commenced this w^ork there were about seventy species of 
fossils known in the rocks of New-York, from the Pottsdam sand- 
stone to the Hudson river group, inclusive. In 1844 I began to 
devote myself to the study of the fossils of these strata j and in 1847 
published the first volume of the Palaeontology, containing three 
hundred and eighty-one species from the same strata. It will be 
readily seen, therefore, that the knowledge derived from the geologi- 
cal investigations alone, up to that time, gave us but a very imperfect 
idea of the extent of this part of the subject. It was only after the 
rocks began to be carefully examined that we had any conception of 
the extent or magnitude of the undertaking. It was impossible to* 
form an idea of the approximate number of species which would be 
