JEFFERSON COUNTY. 



:]85 



havin"' the parts in relief. Hence only under the most favorable circumstances is the outride 

 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 wiiole animal kingdom, in its mode of growth, and in a variety of facts 

 connected with its organization. It ceases to exist with the birdscye 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 now 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 whicli 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, ElUpsolites (No. 1), I have observed in 



1. Kllipsolilcs? 



2. Strophomena UbvIs. 



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 within a chasm for some part of the distance after it enters upon this rock ; but as there 



Geol. 2d Dist. 49 



