372 
[Assembly 
Were it not that quarrying for limestone is carried on to the greatest 
extent upon the Mohawk, incidentally furnishing thin layers of lime- 
stone for flagging, and at a cheap rate, those of the black slate would 
be sought for, being thin, level and smooth. They may be obtained in 
almost all the water courses which flow over the lower part of the 
black slate in Herkimer county, on both sides of the Mohawk. We 
noticed some very excellent ones back of Little Falls, near Stephen 
Hammond's, not far from the old road to Fairfield. Near to these flags, 
in a small water course, at a higher level in the slate, there are two thin 
seams of sulphate of strontian, of a bluish colour and fibrous texture. 
In the thickest seam, which is about the third of an inch, that mineral 
shows in some parts a mixture with carbonate of lime in all proportions. 
There is also near to the strontian, a thin layer of greyish shale which 
when wet with water, separates into parts like lime in slaking. 
In the upper part of this rock, fossils are extremely rare ; but not so 
in the lower part. There we meet with many common to the Trenton 
limestone, such as Lingula ovata, Isotelus gigas, Fucoides dentatus. 
This latter fossil is rare comparatively in the Trenton limestone, but is 
extremely abundant in the Black slate and associated with the Fucoi- 
des scalaris. There are a few fossils which are peculiar to this rock 
besides the last mentioned one, among them is the Triarthus Beckii, its 
characteristic trilobite. 
The small veins of Lead ore and pyrites, on the creek near Spraker's 
basin, are in the Black slate. 
Frankfort slate. This rock or mass is the successor to the Black 
slate ; the one changing to the other by imperceptible gradations, the 
dark or black colour of the lower rock disappearing in the lighter co- 
lour of the upper rock. This rock may be seen to the greatest advan- 
tage on Frankfort creek, back of the village from whence it takes its 
name, and also on the waters of the creek which flow by Utica to the 
southeast of the city, being interposed between the Black slate which 
there forms the bed and sides of the Mohawk and the " millstone grit," 
in consequence of the absence of the next three rocks. 
The upper part of the Frankfort slate in many places alternates with 
thin layers of a fine grained sandstone, more or less intermixed with the 
matter of the slate ; both by long exposure to the air assume a dark 
green or olive colour, by which they are readily distinguished from the 
Black slate, which changes to a brown. 
