LOWER ROCKS AND GROUPS. 
27 
A. Primary. 
B. Potsdam sandstone. 
C. Calciferous sandrock. 
D. Black-river limestone. 
E. Trenton limestone. 
F. Utica slate. 
G. Hudson-river group. 
H. Grey sandstone and Oneida 
I. Medina sandstone. 
K. Clinton group. 
a. Lake Ontario. 
L. 1. Niagara group. 
M. Onondaga-salt group. 
N. Helderberg series. 
O. Hamilton group, including Marcellus slate and 
Moscow shale. 
e. Tully limestone. 
P. Portage group and Genesee slate, 
conglomerate. R. Chemung group. 
S. Old Red system. 
T. Conglomerate of the Carboniferous system. 
The distance upon the north side of the lake has been much shortened in proportion, in order to give more room for the 
rocks upon the south side. 
The same order of succession as here exhibited in the lower rocks and groups, may be seen 
upon the northern shore of the lake between Gananoqui on the St. Lawrence, where the Pri¬ 
mary and Potsdam sandstone are in juxtaposition, and Toronto, where the Hudson-river group 
forms the only rock of the neighborhood. The Calciferous sandrock, Black-river and Trenton 
limestones, are seen at intermediate points, covering extensive tracts in the neighborhood of 
Kingston, Bay of Quinta, and other places. From the point where these rocks leave the 
northern shore of the lake, they trend northwesterly; appearing upon the north side of Lake 
Huron, and thence extending westward to the Mississippi river. 
1. Potsdam Sandstone. 
The Potsdam sandstone is the lowest known sedimentary fossiliferous rock ; it appears in 
the Second district as a mass of great importance, and flanks the great Primary range or 
nucleus on the east, north and west, and rests directly upon the hard crystalline strata, as may 
be seen by reference to the Geological map. It is usually of a pure quartzose character, 
generally grey, though often striped, and sometimes partially or entirely red. From its proxi¬ 
mity to rocks of igneous origin, it frequently assumes a slaty or gneissoid structure ; and it 
is not improbable that sometimes, in favorable situations, it becomes so completely disguised 
as to be mistaken for a gneissoid or granular quartz rock. In places it appears as a conglo¬ 
merate, but in all the localities examined on the north of Lake Ontario, the enclosed masses 
are angular, showing them to be near their origin. This is an extensive rock, known as before 
stated in New-York, Canada, and, from Dr. Lloughton’s researches, on Lake Superior; and 
from position it is probably the same which appears on the Mississippi river, and mentioned 
by Dr. Owen in his Report on the lead region of the northwest. 
This rock is No. 1 of the Pennsylvania Survey, being common to that State, New-Jersey 
