LOWER ROCKS AND GROUPS. 
31 
The change in organic remains at the termination of this group is very great, scarcely one 
of the same species being known to exist in the higher rocks. It thus becomes an important 
point, and well entitled to be considered as the line of division between the lower and higher 
portions of this great system. 
7 & 8. Oneida Conglomerate, and Grey Sandstone. 
In the eastern part of the State, the Hudson-river group is succeeded by a quartzose con¬ 
glomerate ; while in the western part, a grey sandstone occupies the same place. The con¬ 
glomerate forms the Shawangunk mountain, and the mass in Oneida county and in Pennsylvania 
attains a much greater thickness. It is not seen in place west of Oneida, though it appears 
in boulders * scattered upon the surface. The Grey sandstone succeeds the Hudson-river 
group in Oswego county, there being a gradual passage from the one to the other. It is in 
character a grey quartzose sandstone, fine grained and compact, entirely destitute of fossils 
except a few fucoids, thus forming a contrast with the mass below. 
Passing upward, the Grey sandstone intermingles with the Medina sandstone, which in its 
lower part differs from that, chiefly in color, but its upper part contains peculiar fossils. The 
red color of the Medina sandstone seems in some places to be partially communicated to the grey 
below, which is often striped and spotted with red. There is lithologically no very strong line of 
demarkation between the two rocks ; thus offering a gradual passage from the Hudson-river 
group to the Medina sandstone, which might perhaps with propriety be included in the lower 
division. The chief difference is in color, and the occurrence of a few fossils not found below. 
The latter rock forms the lowest mass of the Fourth district, and its connexion with those 
below has been briefly explained; the short notices being intended merely for reference as to 
order of succession, characters of strata and fossils; while for the details of each mass, the 
other reports will be consulted. 
The section shows the absence of three members: the “ Grey sandstone,” the Hudson- 
river group, and Utica slate. The whole width of the lake from the Genesee river northward, 
is excavated in the lower part of the Medina sandstone, and the whole of the three groups 
enumerated. Farther west along the southern shore of the lake, pebbles and worn fragments 
of the rocks of the Hudson-river group, containing the common fossils, occur in great num¬ 
bers. 
To the south of the lake, the section exhibits the rocks of the Ncw-York System, from the 
Medina sandstone upwards, in their order of succession, and also their connexion with the next 
higher masses. In this order, the different rocks and groups will follow in the succeeding 
chapters. 
* See Report of Third District: Oneida conglomerate. 
