Notes upon the Geology of the Western States. 59 
which commences in the eastern part of New York, a very in- 
significant mass, acquiring a great thickness, and becoming the 
most prominent limestone ; the salt group, almost entirely thin- 
ned out, or so far as to be generally overlooked ; and the great 
mass of the Helderberg limestone, so. far thinned out-as to ap- 
pear an integral part of the Niagara mass, and if we did not know 
that in the state of New York it is separated by one thousand 
feet of rocks, indicating an enormous period of time as having 
elapsed between the termination of one and the commencement 
_. of the other, it might seem right to merge it in the Niagara 
; di 
_ Farther westward, in the northern part of the state of ings 
i - and.in the territories of Wisconsin and Iowa, the Niagara lime- 
‘stone becomes still more important, increasing as far as the Mis- 
sissippi river, where it is several hundred feet thick, and actord- 
ing to Prof. Owen’s report, from barometrical observations made 
by Dr. Locke, five hundred and fifty feet. This statement I am 
able to verify to a great degree, but the uppermost one hundred 
feet should be credited to the Helderberg group, and to the cor- 
nitiferous mass of Eaton, which caps many of the high mounds 
of this region. (Throughout this great extent of country and for 
many miles west of the Mississippi, the upper beds of the true 
Niagara limestone are characterized by containing the Catenipora 
escharoides, and often a Retepora, above which are the thin mass 
of water-lime and the fossiliferous portions of the Helderberg 
group. .The Catenipora i is the characteristic fossil. of the upper 
part of the Niagara limestone in western New York, and so far 
as I know is confined to this rock. Its geographical range is 
therefore immense, when we consider the small thickness to 
which it is restricted. 
_ The thickness of the Niagara limestone is not its most impor- 
tant character. It proves on examination to be the lead-bearis 
rock of the west, a fact which I had previously anticipated from 
the same rock every where containing the sulphurets of lead and 
zinc in western New. York—sometimes in isolated particles or 
small masses, or here and there a few crystals in a cavity, or in 
thin veins in what appeared like fractures or fissures in the rock ; 
in truth, presenting the aspect of a metalliferous rock, and indu- 
whe the belief that under the proper conditions it might become 
y so. ASS out of view the limits of dieazintp or states, 
= 
