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 rockSj 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 

 limestone. 



Farther westward, in the northern part of the state of Illinois, 

 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 accord- 

 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 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-bearing 

 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- 

 cing the belief that under the proper conditions it might become 

 highly so. Leaving out of view the limits of districts or states, 



