04 NEW YORK STATE MUSEUM 



samples saved do not suffice properly to identify the rocks. The 

 confusion which exists is in the pro^^er discrimination of the Pots- 

 dam from the Beekmantown on the one hand, and from the pre- 

 Cambrian on the other. The basal Beekmantown is often very 

 sandy ; and the light colored pre-Cambrian gneisses will furnish a 

 rock powder exceedingly difficult to distinguish from the Potsdam 

 excejjt by the most searching microscopic examination, possibly 

 not even by that. Thus the earlier interpretations of the Globe 

 and Campbell wells assigned from 300 to 400 feet of the rock 

 passed through to the Potsdam. Prosser's later study of the 

 Rome well led him to the belief that the Potsdam was not present 

 there, the Beekmantown resting on the pre-Cambrian, with a total 

 thickness of 475 feet. But the basal 275 feet of the rock referred 

 to the BeekmantoAvn seems not at all calcareous, so that its 

 reference to the Beekmantown is somewhat problematic. Litho- 

 logically it certainly does not belong there. On the other hand, 

 as Prosser points out, it is very probable that much, if not all of 

 the rock referred to the Potsdam in the two Utica wells may in 

 reality be pre-Cambrian.^ 



As might reasonably be expected, the Ilion well exhibits a sec- 

 tion very like the surface section at Little Falls. The Beekman- 

 town is a little thicker, but it shows calcareous matter down to 

 its very base, just as it does at Little Falls. Since Ilion and Little 

 Falls show such similar sections, though 9 miles apart, it is exceed- 



^Through the kindness of Professor Cusliing, I have had the opportunity 

 of reading the above remarks concerning the Beekmantow^n limestone 

 in the Rome well. Data obtained after the preparation of my paper on 

 " Gas-well Sections in the Upper Mohawk Valley and Central New York " 

 leads me to accept fully Professor Cushing's conclusions. Of the 475 feet 

 referred to the Calciferous [Beekmantown] formation in the Rome well (loc. 

 cit. p.139, 140, 143), I would now refer the upper 190 feet, from 1085 to 

 1275 feet in depth, to the Beekmantown limestone. The lower 285 feet, 

 from 1275 to 1560 feet, are apparently not calcareous and are composed 

 mainly of quartz sand. It is not improhahle that part of this thickness, 

 and perhaps all, belongs in the Potsdam sandstone; but I am inclined to 

 think that it is a difficult matter to say Avhere the line between the 

 Beekmantown and Potsdam formations shall be drawn. 



C. S. Pbosser 

 Mar. 10, 1902 



