62 Notes upon the Geology of the Western States. 



The result shews very clearly that there are two great lime- 

 stone formations occupying the valley of the Mississippi, and 

 that the lead-bearing limestone is not the same as that immedi- 

 ately underlying the coal formation.* In some places, both these 

 limestones are very similar, and in the absence of the neighbor- 

 ing rocks or fossils, might be mistaken without careful observa- 

 tion. Both are often light colored, a fact which is common to 

 nearly all the western rocks as compared with those of New York. 

 From the light color and magnesian character of the Niagara 

 limestone, it has been erroneously considered as holding the place 

 of the magnesian limestone of Europe, the true position of which 

 is known to be above the coal formation. 



The facts here stated show a great diminution, first of sandy 

 matter, and next of shale, as we go westward, and in the whole, 

 a great increase of calcareous matter in the same direction. A 

 large portion of that mass known as Medina sandstone is shale, 

 and in New York is of great thickness, while it has entirely dis- 

 appeared westward. The Onondaga salt group, essentially a 

 clayey or shaly one, is in its greatest force in central New York, 

 while it is entirely wanting westward. The fossiliferous shales 

 of the Ludlowville group, as already stated, are at the falls of the 

 Ohio, represented by a little more than one hundred feet, and far- 

 ther west by still less. Again, all those of the Gardeau, Portage, 

 and Chemung groups, seem almost obliterated and to give place 

 to an enormous mass of limestone, which goes on increasing 

 westward as far as known. 



The name "cliff limestone," of Prof. Locke, is very appro- 

 priate for what I have here termed the Niagara limestone, so far 

 as the western part of Ohio and part of Indiana are concerned, 

 and I own that after examining these districts I was much grati- 

 fied with the name. But after seeing a limestone much higher 

 in the series already described, forming cliffs for several hundred 

 miles along the Mississippi, the name seems of doubtful propriety. 

 The name "scar" or cliff limestone of English authors, is ap- 

 plied to one much higher in the series than that alluded to, so 

 that the name having once been used for another rock, renders 

 its adoption for this improper. 



Albany, September 16, 1841. 



The lead-bearing rock of Missouri is a different one from that of Iowa, Wis- 

 consin, and Illinois. 



