JEFFERSON COUNTY. 
385 
having the parts in relief. Hence only under the most favorable circumstances is the outside 
preserved, and this exhibits a structure which belongs only to animal forms. 
I should not have occupied so much time and space with this fossil, were it not one of the 
most interesting in the whole animal kingdom, in its mode of growth, and in a variety of facts 
connected with its organization. It ceases to exist with the birdseye limestone ; and in some 
places in the Mohawk valley, particularly at Fort-Plain, it lives up to the trenton, but it 
ceases precisely at the line of junction between the two rocks. Not a branch or twig appears 
above the upper surface of the last stratum of the birdseye, and by no possible means could 
this fossil be discovered in a higher geological position. Upon the very last stratum, some of 
the most characteristic fossils of the trenton are deposited ; and from this platform, a new 
order of events take their rise, or a new series of beings date their beginning. 
Of the Crustacea belonging to this rock, a calymene appears to be quite common on the 
Black river, particularly at the Great bend. A figure of the tail of a species is given, in 
p. 276, No. 3. This is the only part which I succeeded in obtaining in any degree of per¬ 
fection. Of the stone corals, one small cyathophyllum is met with, but it does not appear 
abundant. A bivalve shell, a strophomena, (Fig. 97, No. 2), is quite common at the Great 
bend. Of the univalves, one named by Mr. Conrad, Ellipsolites (No. 1), I have observed in 
97 . 
several places. It is generally exposed by the weathering of the surface, but the structure is 
never brought out in sufficient perfection to show the entire form of the fossil. 
Though this rock appears usually so meagre in fossils, yet a closer examination of it at 
numerous places will satisfy us that they are by no means wanting in it, but the peculiar 
structure of the rock forbids their exposure and detection in the ordinary way. 
Descending from the village of Watertown to the west, along the whole mass of the trenton, 
and the seven-foot tier, as it is termed by quarrymen, we pass from these rocks successively 
to the birdseye. Each in its turn has been removed by abrasion, down to the latter, which 
forms the surface rock in the direction of Brownville to the lake, with the exception of a 
narrow ridge. At and below this village, the river flows through a deep rocky chasm formed 
of the birdseye. 
The whole thickness of the birdseye in the county is not far from thirty feet. Neither at 
Watertown, nor at any point above, is it possible to determine its thickness. The river flows 
along wdthin a chasm for some part of the distance after it enters upon this rock ; but as there 
Geol. 2d Dist. 49 
