On the Silurian System of the Lake Superior Region. 191 
There is another question which may arise, and that is, as to 
the relations of the lead-bearing rock to the Hudson river group; 
for there appears to be little probability of identifying this group, 
at any of the localities west of Lake Michigan. If the upper, 
near Galena. 
_({Mr. Hall next describes the Upper Silurian’ and Devonian Se- 
nes, showing that the region presents strata of the Clinton Group, 
Niagara Group, Onondaga Salt Group and upper Helderberg Se- 
nes. The Medina Sandstone which occurs below the Clinton 
Group was not recognized. The Clinton Group oceurs at Drum- 
mond’s Island, along the eastern shore of Green Bay, on Stur- 
geon Bay, and probably about Lake Wiunebago. ‘To the south- 
West of Green Bay near Hartford, there is a band of oolitic argil- 
laceous iron ore, similar to that of the Clinton Group in New 
York. Beyond the entrance to the Bay des Noquets, fossils of a 
Species of Cytherina, an Avicula and Murchisonia subulata were 
observed ; and at Sturgeon Bay, the Pentamerus oblongus. The 
Clinton Group becomes calcareous to the west; while in central 
New York it consists mainly of shaly and arenaceous beds, wit 
Very subordinate layers of calcareous matter, at the Niagara river 
itis made up of two members of limestone and one of shale. 
= closing his remarks on the Niagara Group, Mr. Hall ob- 
tves] :— 
Notwithstanding all the changes which have taken place in the 
Niagara group, as developed at different points, and its intimate 
blending, as in this district, with the limestone of the Clinton 
stoup below and the Onondaga salt group above, we find no se- 
nous difficulty in recognizing it as a whole, both by lithologica 
characters and fossil remains. We have been able, by these 
characters combined, to trace its continuation throughout the en- 
Ure district from east to west. We have seen it, in this extent, 
assuming different aspects, dependent on causes before adverted 
‘0; but we have never failed to find a greater or less number of 
Known characteristic fossils, even where the strata were explored 
only to a limited extent. Their occurrence, under such circum- 
