THE SECTION POTSDAM SANDSTONE 



159 



ward and southward, so that the thickness is not greatly ih excess of the 

 irregularity of the surface upon which it was deposited. It is therefore 

 thickest over the old valleys and thinned over the ridges, some of wliose 

 summits it failed to overtop. 



7 

 6 



, - 1/ - /'f -, f 



^^^ 



^^m\ 





3 - iif' -~i?r 



- », - IT 



ITZH: 



E?:?^=T^^r^?^ 



a^^gE^ 



A A^a^aA-aI 



Feet 

 7. Trenton limestone. Thin bedded, blacli, 

 somewhat shaly limestones, with 

 lenses of gray, crystalline limestone. 



6. Black River limestone. Massive black 

 limestone, lower portion full of black 

 chert nodules 15-20 



5. Lowville limestone. Blue or dove-colored 

 fine-grained limestone, with beds of 

 thin shaly limestones, which consti- 

 tute nearly one-third of the forma- 

 tion 75-85 



4. Pamelia limestone. Blue and dove lime- 

 stone, with intercalated magnesian 

 limestones and, in the upper half of 

 the formation, much whitish, impure 

 limestone and some yellow water- 

 lime. A thin basal sandstone and 

 overlying shales 40-130 



3. Theresa formation. Somewhat calca- 

 reous, sandy dolomites, weathering tu 

 rotten stone, with interbedded weak 

 sandstones, especially near the base. . 20-60 



2. Potsdam sandstone. White, yellow 

 and red quartzose sandstone, brown 

 spotted and weakly cemented toward 

 the summit 



1. Pre-Cambrian. 



0-80 



Figure 1. — Generalized Section 

 of the Rocks of the Theresa 

 Quadrangle. 



In large part the formation consists of a nearly pure and quite thor- 

 oughly cemented quartz sand. It shows local thin conglomerates basally, 

 which become important only in hollows of the old surface. Where the 

 formation rests on Grenville limestone it has sometimes a calcareous 

 cement and is weak, but there is no great bulk of rock of this sort. On 

 the Alexandria quadrangle there occurs a stratum of very coarse con- 

 glomerate several feet in thiclmess, which begins and ends abruptly, has 

 ten or a dozen feet of sandstone beneath it instead of being basal, and is 

 a highly puzzling occurrence.^ 



« C. H. Smyth, Jr. : 19th Report of New York State Geologist, p. r99 and pi. 23. 



