LORRATN SHALES. 
121 
layers of sandstone and argillaceous matter alternating with each other, the latter often ex¬ 
tremely fine, and the former never coarse : mica in minute scales is common in many layers, 
but is not apparent in all. The materials of this formation are quite subject to disintegration ; 
and hence, wherever streams have passed over it, they have, in process of time, worn in the 
rock a deep channel or gorge. In the towns of Lorrain, Pinckney and Rodman, the surface 
is so much channelled by the streams, that a free communication between them is prevented, 
except by circuitous routes. These gorges will be particularly noticed, when I come to speak 
of the geology of Jefferson county. 
Thus far I have been particular in giving the characters of the Lorrain shales and sand¬ 
stones, as they exist in Jefferson county. When, however, we extend our examination to 
distant fields where the same formation prevails, we find a greater diversity of mineral cha¬ 
racter, and that the whole series is not fully represented by the rocks I have just described. 
By reference to section No. 42, it will be observed that several masses, differing mineralo- 
gically from each other, are represented as occupying a position superior to the Utica slate. 
In addition to those strata which have been observed in the gorges of Lorrain and Rodman, 
the following must be considered as belonging to the formation : 
1. Deep red and purple shales, the former fine grained, and without scales of mica ; the latter coarse, and con¬ 
taining mica, approaching a fine grained sandstone. They rarely contain seams of spar, or any imbedded mineral 
substance. 
The position of this variety appears to be inferior to the shales peculiar to Lorrain: at 
least, I have not been able to discover them in Jefferson, or the adjacent counties. We find 
this mass occupying a narrow belt of the shales, which passes through the higher parts of 
Columbia, Rensselaer and Washington counties, and onward through Vermont into Canada. 
It is every where destitute of fossils. It is fine, but sharp-gritted, and is often employed for 
houses. It is durable, and resists the action of weather, and does not split in thin lamina on 
being wet. 
2. Glazed slates .—The mass is composed of flatlened ovoid pieces, but made up of lamina which separate readily 
from each other, and which always leave a fine black glossy surface, as if it had been covered with a black japan 
varnish. It is often mistaken for coal. 
So far as I am able to judge, this variety does not occupy a distinct place in the series, but 
appears to have been produced from the shales by certain movements in and of the mass. In 
is not purely argillaceous, but contains hard siliceous or calcareous particles, which were 
separated from the aluminous matter while in a soft plastic state : these, therefore, became 
the centres of attraction, and formed small ovoid nuclei, which, when the whole was subjected 
to an elevatory movement, produced friction and pressure, so as to give a polish and compact¬ 
ness to all those points where the resistance was unequal. This mass is always in a shivery 
state ; and it is impossible to discover traces which mark, even obscurely, the probable planes 
of deposition. Neither are their joints produced by crystallization, as in most shales; the 
planes, therefore, of deposition, and the natural joints, appear to have been destroyed, or 
broken by a double movement to which the mass has been subjected. The first was un- 
Geol. 2d List. 16 
