JEFFERSON COUNTY. 
399 
As a whole, this rock is less firm and indurated in this county than in the Mohawk valley, 
or upon Lake Champlain. It appears never to have been subjected to so much pressure and 
to such powerful disturbing forces as elsewhere. It presents simply the fragile argillaceous 
slate of authors, without siliceous matter, or beds of shale, as in the succeeding mass. The 
great differences which may be observed, are those resulting from disintegration, which is 
rapidly going on where it contains pyrites. 
This mass contains a great abundance of the fossil common to it elsewhere, the Graptolites 
dentatus (No. 2, p. 279); and it also contains the Trocholites ammonius (No. 3), which, 
however, is rare, so far as my observation extends. A smaller and smoother trocholite is more 
abundant. The species most abundant in this region, arc exhibited in the following cut: 
no. 
1. Triarthus beokii. 3. Cypricardites sinuata. 5. Avicula. 
2. Nuculites scitula. 4. Nuculites poststriata. C. Lingula rectilateralis. 
No. 1. The Triarthus heckii is probably the most constant and characteristic fossil of the 
rock. I have not observed it in the slaty limestone of the trenton, nor in the shales of Lorainc. 
It is abundant in the gorges at Rodman and Loraine, and upon the route from Adams to 
Tylerville, wherever the slate is exposed. The head is the part usually found, which, from 
its peculiar markings, is readily distinguished from the head of the Calymene. 
No. 2. Nuculites scitula, is extremely common immediately below the loraine shales, or in 
the upper part of the utica slate; and as this part is often absent, the peculiar fossils are 
seldom met with. 
No. 4. Nuculites poststriata, is not a common fossil in Jefferson, or at least has not been 
observed very frequently. 
No. 5. Avicula insueta, belongs to the Mohawk valley. I did not find it in the slate of the 
Second district. 
No. 6. Lingula rectilateralis, is associated with the Triarthus. 
The inferior part of the slate abounds less in organic bodies than the superior ; in fact, in 
some districts, as upon Lake Champlain, thick heavy beds appear to be destitute of all of 
them, except the Fucoidcs dentatus. Next in frequency of occurrence, is the Triarthus beckii. 
The remainder of those which I have figured, appear to be confined to the upper part of the 
rock. 
In assigning the limits to this rock, I have been governed wholly by the presence of the 
Triarthus ; and as this occurs associated with all the fossils of which I have given figures, I 
