52 J. J. STP:VEiNSON — LOWER CARBONIFEROUS, APPALACHIAN BASIN 



measurements across Preston county of West Virginia, which adjoins 

 Fayette and Somerset of Pennsylvania, where he measured the Mauch 

 Chunk in Chestnut, Laurel, and Briery mountains, the last being the 

 continuation of the Pennsylvania viaduct. Here the order may be re- 

 versed and his measurements ma}^ be followed southeastwardl}^, that com- 

 parisons may be made with measurements on the Potomac in Maryland. 

 The Cheat River gap through Chestnut hill is about 20 miles south 

 from the National Road locality just referred to. There Doctor White 

 found shales and sandstones, 299 feet; limestones, 110 feet; silicious 

 limestone, 30 feet ; the upper shales containing 10 feet of impure lime- 

 stone at 40 feet above the base. The silicious limestone varies greatly, 

 being only 5 feet, with 10 feet of overlying sandstone at a little distance 

 from the measured section. The sandstone contains fragments of the 

 limestone as at many localities in southwestern Pennsylvania. Under 

 the Laurel Hill axis, on the w^est side, at 30 miles south-southwest from 

 the Youghiogheny gap, the section is 



Feet 



Shales and sandstones 220 



Limestone 94 



Silicious limestone 8 



with the 10 feet of impure limestone persistent in the shales ; but the 

 silicious limestone is as variable as under Chestnut hill, for on the east 

 side of the fold it is 35 feet thick, and the upper part of the Pocono 

 sandstone is calcareous for 10 or 15 feet. At this last exposure the 

 shales are 295 feet, with a thin coal bed within the top 25 feet, while 

 the upper limestone has become 120 feet, an increase eastwardl3\^ On 

 the west side of the Briery axis, 15 miles south from the last and about 

 30 miles west from Westernport, in Maryland, the whole mass is thick- 

 ened greatly, for there the section is 



Feet 



Shales and sandstones 370 



Limestone and thin shales 227 



Silicious limestone 105 



Shale 10 



No limestone appears here in the upper shales, as the impure lime- 

 stone of the Cheat river sections has become 20 feet thick, and is included 

 in the limestone mass. The limestone division is less pure than in the 

 Cheat sections, and is broken up into eight beds, aggregating 124 feet 6 

 inches, separated by beds of red and green shales from 4 to 20 feet thick, 

 so that while there has been an increase in thickness of limestone, that 

 in detrital matter has been still greater. No sandstone occurs in the 



*l. C. White: Proc. Amer. Phil. Soc, vol. xx, 1882, pp. 484, 486, 491, 492. 



