184 



INDEX TO THE STEATIGRAPHY OF NORTH AMERICA. 



Dana^^" distinguished "Calciferous epoch, Chazy epoch, Trenton epoch, Utica 

 and Hudson epochs" and described the strata which characterize each epoch in 

 this and other districts. The New York State Survey pubhshes the following 

 classification,^®^ which shows also the distribution of the several divisions and 

 brings out the fact that they are not uniform throughout the State. 



Extent of unit formations along their strilce from west to east in the State of New YorJc. ["] 

 [A star (*) signifies that the unit is absent from the outcrops in the region represented by the column in which it stands.] 



" Revised in accordance with letters from John M. Clarke, Jan. 13 and 19, 1910. — B. W. 

 b The Frankfort begins well down in the Trenton and extends upward to some undetermined age. 

 corresponds to the Martinsburg shale. — E. 0. Uhich, comment on manuscript. 



Possibly it 



Grabau ^*^ published a discussion of the Ordovician in 1909 and suggested a 

 revised classification. 



It appears from the investigations of recent years that the Ordovician lime- 

 stones west and south of the Adirondacks, like those of the upper St. Lawrence 

 Valley, differ from the formations of corresponding age that occur east of the Hud- 

 son-Champlain trough. The western strata were spread over the margin of the 

 continent in embayments that extended north and south of the Adirondack island 

 or peninsula. They are neither uniform in distribution nor continuous in sequence. 



Gushing ^'^^ has recently worked in Lewis and Jefferson counties west of the 

 Adirondacks, in the original locaUty of the Lowville (or "Birdseye"), Black River, 

 and Trenton limestones, to which Logan refers as quoted above (p. 183). He there 

 determined the following section: 



Feel 

 7. Trenton limestone: Thin-bedded black, 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 constitute nearly one-third of the fornjation 75-85 



4. Pamelia limestone: Blue and dove limestone, 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 



[Unconformity.] 

 3. Theresa formation: Somewhat calcareous, sandy dolomites, weathering to 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 '. (>_8o 



1. Pre-Cambrian. 



