370 
[Assembly 
ing from the mixed mineral nature of the layers, may be confounded 
with those of the fucoides. The fucoides are yet undetermined. 
The best localities along the Mohawk for the examination of these 
layers are the falls on the creek near Spraker's basin, and by the side 
of the rail-road, opposite to Fort-Plain — greatest thickness about thirty 
feet. 
Mohawk limestone. This is the rock so extensively quarried for the 
enlarged Erie canal at Amsterdam, Canajoharie, Fort-Plain and other 
places along the Mohawk river, also along the Black river, for the use 
of its canal. Its layers are thick, solid, easy to work from being some- 
what brittle, but for hardness and solidity must form very durable ma- 
son work. 
Its associates are the water lime of Lowville on the Black river. At 
Canajoharie some of its layers contain a greenish matter analgous to 
" green earth ;" others are brownish and sandy, probably from union 
with the fucoidal layers below them. 
It contains no metallic mineral, if we except a little iron pyrites, of 
which very few of the New- York rocks in any locality, are entirely 
destitute. Greatest thickness about 40 feet. 
Its characteristic fossil is the orthostoma communis ; there are seve- 
ral others, none of which have yet been described or named. In this 
rock we first meet the genus Cytherina. The individuals, however, are 
but few in number. 
Bird's eye" liinestone. This rock is confined almost entirely to 
the Mohawk valley, and invariably where it exists, it rests upon the 
last mentioned limestone, forming the upper layers (from memory) of 
all the quarries to the west of Canajoharie, embracing those on East 
and West Canada creeks, with the exception of the quarry on the south 
side of the river west of Little Falls. 
This rock is eminently characterized by the fucoides demissus which 
is often replaced by crystalline limestone, and sometimes by black and 
by green mineral matter, which exhibits the outlines of the fucoides in 
strongly marked characters. When the taste of our citizens shall in- 
cline them to simple colours, like the drab and dove, then the "bird's 
eye" and the Mohawk limestones will be resorted to for marbles, from 
the beautiful shades of these colours which they present. 
