No. 275.] 
315 
From Penn-Yan to Seneca lake, the southern limit of the upper 
black shale is the right bank of the outlet, where both this and the 
succeeding rocks are seen to crop out. The present outlet has cut itself 
a channel through the upper black shale, the Tully limestone, and about 
one hundred feet into the shale below. 
Northwesterly from Penn-Yan to Shepherd's quarry and the adjoining 
ravine, we find the group of argillaceous sandstones and shales next 
succeeding the black shale. At this place the lower portion of the 
mass consists of hard and soft strata, containing much iron pyrites and 
large fragments of carbonized vegetables; and occasionally other fossils 
which are characteristic of the group, as the large Orthocera and a 
Pterinea. Above this are thirty or forty feet of shale, containing Posi- 
donia in great abundance, and embracing a single layer of striped 
sandstone. This shale is succeeded by two layers of sandstone, and 
these are again followed by a thick mass of shale. 
The lower part of the group furnishes large and fine flag stones, 
which are used in the streets of Penn-Yan. These thin layers often 
contain small irregular concretions, surrounded by a coating of shale 
which soon disintegrates and the concretions become loosened, in many 
instances injuring the stone. Some of these strata are shaly and soon 
wear away on exposure. 
This group appears about a mile south of Penn-Yan, in SartwelPs 
ravine; w^here its connection with the black shale below is very evident; 
the characteristic Lingula of the latter are found in abundance, and suc- 
ceeded by a thick mass of more silicious, non-fossiliferous shale. 
The same group extends west through the towns of Jerusalem and 
Italy, and appears in many of the streams and ravines near the west 
branch of Crooked lake. The thin layers of sandstone are used 
throughout the country for step-stones, foot- walks, and in many instan- 
ces for enclosures, though rarely for building stones. 
It is chiefly along Crooked lake outlet that we find any rocks below 
the groups last described. Here, in the descending order, are the black 
shale, the Tully limestone, and the upper member of the group next 
below, (Moscow shale,) consisting of bluish or olive and dark shales 
with an abundance of fossils. Descending the outlet about a mile and 
a half from Penn-Yan, the black shale first appears, forming both 
banks of the stream as far as Mallory's mills, sometimes rising forty or 
fifty feet above the bed of the stream, and at others merely visible beneath 
