UTICA SLATE. 
117 
not seem to have survived the changes which took place between the deposition of one rock 
and the other ; though, judging from an inspection of the two mass.es, nothing 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 either 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 the Utica slate, is the Triarthus beckii, a remarkable crusta¬ 
cean, which appears to be confined wholly 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, having 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 the 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 : 
Lower Limestone. 
Shales and Slates. 
42. 
Shaly Sandstone. 
Medina Sandstone. 
1. 2. 3, 
1. Chazy limestone ; 
2. Birdseye ; 
3. Marble of Isle La Motte 
4. Trenton limestone 
4. 5. 
5. Utica slate; 
C. Lorrain shales ; 
7. Red and purple shales ; 
8, Glazed slates; 
7. 8. .a. 9. 
a. Calcareous breccia; 
9. Grey sandstone and conglomerate; 
b. Thin beds of limestone; 
10. Medina sandstone and marly sandstone. 
The Utica slate weathejs 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 
