No. 136.] 



41 



known in the Mohawk valley, as also along the Black river and 

 Lake Champlain : it is a fine-grained gray brittle limestone, thirty 

 feet in its greatest thickness ; and the most conspicuous of its 

 fossils is one the nature of which is somewhat obscure, but which 

 is believed to have been the stems of some marine plant. Stand- 

 ing in an upright position, perpendicular to the strata, the ends 

 of the stems are seen on the surfaces of the layers, to which they 

 give a peculiar dotted appearance, from which the rock has 

 derived its name 



BIRDSEYE LIMESTONE, 



and by which, as well as by its characteristic color and fracture, 

 it is easily recognized.* It is a valuable rock for economical 

 uses, as it is a good building stone, and dresses well under the 

 chisel ; and it is quarried to a considerable extent at various 

 points in the Mohawk valley. 



The only fossils of this rock, beside the peculiar plant above 

 mentioned, are an Orthoceras (Fig. 5) and a few species of coiled 

 and spiral shells, not common, and generally obtained only in bad 

 preservation. 



To the Birdseye limestone succeeds a thin mass, amounting in 

 all to only ten or twelve feet, but classed as a distinct rock from 

 being marked by having a somewhat peculiar mineral character, 

 and containing a peculiar set of fossils. It is a dark, thick- 

 bedded, compact, hard limestone, fine-grained and taking a high 

 polish, and is worked as a black marble at Glen's Falls on the 

 Hudson, and at Isle La Motte on Lake Cha'mplain. It is also 

 well seen at Watertown, Jefferson County, in the river banks, 

 from which locality it has been named the 



BLACK-RIYER LIMESTONE. 



In the last named place it is lumpy and irregular in texture, and 

 not fit for good masonry or marble ; and is known among the 

 quarry men as "the seven- foot tier." In the Mohawk valley it 

 seems not to have been deposited except in a few places, the 

 Birdseye being generally covered directly by the Trenton lime- 

 stone. 



The most abundant and remarkable fossils of this rock are 



* Fig. 4 represents the general appearance of this fossil as seen on the broken edges of the 

 layers, where its upright stems are visible. 



[Assembly, No. 136.] 6 



