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[Assembly 
trict. It may be termed crinoidal limestone, ^^par excellence, for the 
stems of encrini are often one or two feet in length, and many of them 
an inch in diameter. This mass has often been mistaken for the TuUy 
limestone, in the western part of the State, and thus given rise to some 
confusion regarding the rocks above and below ; but this difficulty I 
have been able to explain. All the cited localities of the Tully lime- 
stone, west of the Genesee river, exhibit only the crinoidal limestone, 
and instead of being between the Moscow and upper Black shale, is 
below the Moscow, and between it and the Ludlow ville shale. This 
fact readily accounts for the highly fossiliferous shale above the sup- 
posed Tully limestone on Lake Erie. 
The group mentioned in the report of last year as succeeding the 
upper black shale, and consisting of sandstone, shale, &c. developed 
* on Cayuga and Seneca Lakes, and more particularly at Penn-Yan, be- 
comes on the Genesee, a mass of green crumbling shale, of one hundred 
and ten feet thickness. It is exposed on the Cashaqua creek, above the 
junction of the Genesee Valley canal and the Dansville branch, and at the 
Shaker's Mill, on the same stream ; hence the name of Cashaqua shale. 
When first quarried this rock appears in thick masses, which, after 
a little weathering, falls into cubical or angular fragments. It contains, 
occasionally, thin concretionary layers of sandstone ; these are not con- 
tinuous, and may be no essential feature of the rock. The fossils are 
two or more species of Cyrtoceras, a large and beautiful species of 
Pterinea, Orthis, Posidonia, &c. 
In the order of succession the Ithaca group follows the Cashaqua 
shale ; but in the Genesee valley, and the counties examined this sea- 
son, that group is entirely wanting, and will prtbably not be identified 
farther west than Seneca Lake. The Cashaqua shale is succeeded by 
a thick mass of shale and flagstones, or thin strata of sandstone, at in- 
tervals of a few feet, and often a few inches. The sandstone layers 
do not often exceed six or eight inches, and generally are not more 
than four inches in thickness. In the lower part of this mass the un- 
der surfaces of the sandstone are covered with large straight fucoides, 
and often present the appearance of having been deposited on a surface 
of shale, which had previously been smoothed and slightly scratched 
by running water, bearing light and fine materials in its current. 
Throughout the greater part of this group the lower surfaces of the 
sandstone strata are covered with short, rigid fucoides, of the size of a 
