390 
GEOLOGY OF THE FIRST DISTRICT. 
2. Utica Slate. 
Synonims. Mohawk slate, Black slate and, shale, Fairfield slate, Graptolitic slate, of the Geologi¬ 
cal Reports of New-York; Transition argillite, Wacke slate, and Glazed slate, of Prof. Eaton’s 
works. No. 3 of the Pennsylvania Survey. 
Fig. 24. 
a 
1. Triarthus beckii. 2. Graptolites dentatus. 3. Trocholithus-. 
The rocks of this group consist of dark colored argillaceous slates of several varieties, in 
different parts of the First geological district. In the valley of the Mohawk above Schenectady, 
in Saratoga county, west of the main anticlinal axis, and between Fort-Ann and Glensfalls, 
it is scarcely disturbed from the position in which it was originally deposited; and there it 
shows its unaltered characters of a dark colored slate, frequently loaded with carbon, and con¬ 
taining various genera and species of vegetable and testaceous fossils. It is interstratified 
with thin bands of limestone, and sometimes also with thin layers of carbonate of iron as 
subordinate strata, and it passes into the Trenton limestone by gradual inter stratification. 
Thin bands of slate are interstratified in the limestone, and thin strata of limestone in the 
lower part of the slate containing fossil remains. The Triarthus heckii, and several other 
fossils, were found in one of these bands of limestone. The slate in mass, in its lower portion, 
is calcareous. 
On the east side of the main anticlinal axis, the strata of this group are generally similar, 
and contain the same fossil remains, but differ by frequently presenting the slaty cleavage 
distinct from strata planes or planes of deposition ; by being upturned at every angle to the 
horizon, crushed, shivered, and contorted in the most extraordinary manner; and by being 
frequently altered in texture by causes that have produced the above mentioned effects. The 
glazed slate of Prof. Eaton is a variety of this slate, in which the small fragments into which 
it breaks in consequ^ce of its having been shivered, are coated with a black glazing, having 
the appearance in some localities of a thin film of anthracite. Another modification of this 
slate, which is quite common on the east side of the Umdson, and is not uncommon on the 
west bank east of the anticlinal axis, is siliceous slate, varying in character from basanite to 
common siliceous and flinty slate. It is red, green, brown, black, and of various intermediate 
shades of color. 
