UTICA SLATE. 



117 



not seem to have survived the changes which look place between the deposition of one rock 

 and the other ; though, judging from an inspection of the two masses, notliing worthy of notice 

 can be observed, which indicates a material difference in their composition, or in the circum- 

 stances attending their deposition ; still, such is the change that the beings which flourished 

 in great numbers during the Trenton era, are apparently swept out of existence, and their 

 places supplied by new forms, a few new genera, or new species. 



In general, there is a scarcity of fossils in the rock under consideration ; the actual number 

 of individuals of the species which are found in it, are much less than in cither of the rocks 

 below. The change, therefore, from one rock to another, is remarkable, and must have been 

 produced by causes acting generally, for the above facts are found to prevail wherever the 

 rocks have received a careful examination. 



The characteristic fossil of tlic Utica slate, is the Triarthus beckii, a remarkable crusta- 

 cean, which appears to be confined wliolly to this mass. I have neither seen it in the Trenton 

 slate below, nor in the Lorrain shales which overlie it ; yet it is constantly present in this 

 rock, havi7ig found it in the shales above Glen's Falls, at many places in the valley of the 

 Mohawk, and at the Falls of Montmorenci. 



Much confusion existed in relation to the geological position of this and the succeeding 

 slates and shales, not only in this country, but in Europe ; they had uniformly been placed 

 below the limestones described in the preceding pages, and adjacent to and immediately upon 

 the primitive rocks. Such, in fact, appears to be the order along tlie western face of the 

 Green Mountain or Taconic range ; but leaving this point for remark hereafter, I would 

 observe, that the Utica slate may be examined to advantage in the Second District, at or near 

 Glen's Falls, or along either shore of Lake Champlain, or to still greater advantage in the 

 gorges in Lorrain and Rodman in Jefferson county. The annexed section is introduced in 

 this place, for the purpose of exhibiting distinctly not only the geological position of the Utica 

 slate, but the whole of the upper series of the Champlain group : 



Lmvcr Limestone. 



Shales and Slates. 



Shaly Sandstone. 



Medina Sandstone. 



1. 2. 3. 



1. Clmzy limestone ; 



2. BirJseye ; 



3. Marble of Isle La Motte 



4. Trenton limestone ; 



5. Utica slate ; 



6. Lorrain shales ; 



7. Red and purple shales ; 



8. Glazed slates ; 



7. 8. a. 9. b. 10. 



a. Calcareous breccia ; 



9. Grey sandstone and conglomerate ; 



b. Thin beds of limestone ; 



10. Medina sandstone and marly sandstone. 



The Utica slate weathers ash grey, and rapidly disintegrates ; and where it is exposed in 

 cliffs, frost and other agents constantly break it into small shivery fragments, which collect at 

 the base in the form of a talus. When once dried, after being removed from the bed, it be- 

 comes firmer and stronger ; but if immersed afterwards in water, it immediately breaks into 

 numerous fragments. It is partly to this effect of water upon the mass, that so few fossils 



