Report oi the State Geologist. 



A noteworthy characteristic of this formation in the county, is the occur- 

 rence of quite pebbly layers at numerous horizons from the bottom to the 

 top. The pebbles are almost invariably of quartz. At the base a few of 

 orthoclase are mingled w ith them. 



The various layers of the rock show great variation in their resistance to 

 weathering. While the major part of the mass is w ell indurated and very 

 durable, there are many layers in w hich the induration is much less, and 

 which disintegrate quite rapidly to a coarse white sand. The most unstable 

 portions are the red beds already mentioned as intermingled with the lower 

 conglomerates. These have a large content of orthoclase derived from the 

 gneisses, are permeated w ith hematite w hose origin is uncertain, and break 

 down rapidly to a red, hematitic, sandy clay, w hich is a very conspicuous 

 feature along some of the roads. 



The absolute thickness of the Potsdam hereabouts has not been 

 determined w ith certainty. As it was deposited on an uneven, probably very 

 uneven, floor, and as this floor was subsiding at the same time, its original 

 thickness must have varied much from place to place. The thickest section 

 susceptible of accurate measurement in the county, is that on the Ausable 

 river w here, according to Mr. C. D. Walcott, there is a thickness of 350 feet, 

 with the base and summit not seen."" The impression conveyed by the wide- 

 spread exposures in the northern part of the county is that the total thickness 

 can scarcely fall short of 2,000 feet, and is quite likely much more. The 

 possible presence of faults increasing the apparent thickness, renders it 

 impossible to speak more definitely. If such are not present, the Potsdam is 

 unquestionably more than 2,<>00 feet thick. 



While it has been impossible to make an exhaustive search for fossils, a 

 sharp lookout has been kept for them, and considerable time spent in the 

 (piest ; vet none have been found except along the Ausable, where their 

 presence has long been known. The Upper Cambrian age of the higher 

 portion of the Potsdam has been shown, but there is as yet a complete lack of 

 paheontologic evidence as to the age of the lower part. 



The, Galdferous sancb-ock. Rocks belonging to this division are spread 

 over a considerable area in the tier of townships along the lake, but are 

 unfortunately so concealed by Pleistocene deposits that the Potsdam Calcifer- 

 OUS boundary is almost completely obscured, and the Calciferous exposures 

 are often disappointing, though excellent sections are exhibited in Beekman- 

 tow n and Peru. Professors Brainard and Seely have carefully studied the 



■c I). WalCQtt, Bulletin SI. United Smteg Geological Survey, p. 343. 



