JEFFERSON COUNTY. 



:}8!) 



There are two other masses insulated mucli in the same way. Thus, crossing from the 

 bay at Sackcl's-llarbor, over to Pillar point, we again conic upon the trcnton, which extends 

 over to the west side, or to Chamont bay. Here again tlio trcnton is excavated deeply ; and 

 after crossing the neck of Chamont bay, we find the shores consisting of the trenton, as far 

 as Cape Vincent. 



From these remarks, the geographical extent of the trcnton will be seen ; and in the details, 

 I have introduced those facts which relate to the causes which have controlled the present 

 extent and limits of this rock, from which it appears that it has been considerably limited, 

 especially in the part which extended north. 



I shall now proceed to speak of the fossils which characterize the trenton limestone. And 

 upon this subject I may remark, that few rocks are so finely distinguished as this ; from the 

 birdseye to the utica slate, it is not only well supplied with organic bodies, but they are 

 limited to this mass, so far at least as it has been examined in New-York. Not one of the 

 fossils of the trenton have been found in the limestones below, and as yet it is (|uite doubtful 

 whether they appear higher in the utica slate or loraine shales. Those which first claim our 

 attention are the crustaceans, some of which figure largely in the fossils of the trenton rock, 

 being found in great numbers wherever it occurs. 





2. Stroiiiiomena dclloidea. 



3. Favosites lycopoclitcs. 



The Isotelus gigas (No. 1), is one of the most persistent fossils of this mass. It, however, 

 happens generally, that it is only obtained in parts, the extremities being very liable to sepa- 

 rate from the body. It may be found at Essex, Plattsburgh, Chazy, Glen's-Falls and Water- 

 town. Some large individuals have been obtained near Glen's-Falls, and in the slialy lime- 

 stone at Plattsburgh. 



