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 jock 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 tlie 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 tlie calciferous sandrpck, those of the Chazy limestone, the birdscye, 

 and the limestone of Isle La Motte, and finally those of the Trenton, each of which arc 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 gi-eat 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, Leptsna, 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 lias 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 Paleontologist 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 



