114 
GEOLOGY OF THE SECOND DISTRICT. 
rial. Its color, in the first place, is a recommendation for certain kinds of architecture ; in 
addition to which, it quarries easily, and works freely under the hammer. A structure built 
of this rock, cannot be distinguished at a distance from the grey granites ; and judging from 
its condition and general characters, it is more likely to endure the weather in a changeable 
climate, than granite. 
As the lithological characters of this rock differ from those preceding it, so it differs almost 
in toto in its organic relics. Some of the genera of animals continue, but the species are dif¬ 
ferent ; and this fact induces me to remark, that sudden changes were probably more fre¬ 
quent in the early periods of sedimentary rocks, than subsequently ; and in illustration of this 
view, I may refer back to the impure beds of limestone which compose the calciferous sand- 
rock. The subordinate masses of this rock are comparatively thin, from fifteen to thirty feet 
thick only; and yet they each bear certain fossils which do not appear in the beds above or 
below, notwithstanding the brief interval which must have elapsed between the successive 
depositions of these beds ; and what renders the view more clear, is the limited number and 
peculiar forms of the species, together with the great abundance of the individuals. We 
should expect from the latter part especially, that in masses comparatively thin, the same fos¬ 
sils would continue from one to the other; but this does not appear to be the case ; certain 
species are more clearly confined to those beds which are only a few feet thick, than species 
ordinarily are in the upper rocks, where they are hundreds of feet thick. But we have, in 
addition to the fossils of the calciferous sandrock, those of tlie Chazy limestone, the birdseye, 
and the limestone of Isle La Motte, and finally those of the Trenton, each of which are per¬ 
fectly well characterized by its fossils, though they are all limestones, and follow each other 
in rapid succession. We have, as it appears, a miniature representation of the great fact first 
noticed by William Smith, (whose country I need not mention,) that strata may be identified 
by their fossils ; and to the northern counties I would direct young geologists for the study of 
geological principles, especially to Clinton county, where, near the village of Chazy, they will 
find the facts and principles I have stated amply confirmed. But I recommend a close exa¬ 
mination of the strata ; for by a hasty one, he would be very likely to overlook the most im¬ 
portant facts here disclosed. 
The fossils of the Trenton limestone will be fully given hereafter ; for the present, I may 
state that they belong to the following genera : Lingula, Orthis, Lepteena, Atrypa, Delthyris, 
Avicula, Bellerophon, Euomphalus, Pleurotomaria, Isotelus, Calymene, Bumastus, Trinucleus, 
and several species of fucoids, graptolites and orthoceratites. 
While the Survey of the State has been in progress, the question has often arisen, to what 
rock in the Silurian System is the Trenton limestone equivalent? This question, in the 
early stage of the survey, could not be answered satisfactorily; for even in England and 
Wales, the lower rocks of this system were not then well understood or well characterized ; 
but so much progress has now been made, that we are able to make a few comparisons, based 
on facts, and upon which we may safely reason. 
Mr. Conrad, the Palaeontologist of the Survey, whose general views are remarkably cor¬ 
rect in the early reports, as it regards the general coincidence of the New-York rocks with 
