20 J.J. STEVENSON LOWER CARBONIFEROUS, ATPALACHIAN BASIN 



The Allegheny i^lateau. — Returning now to the north and following the 

 backbone of the Allegheny plateau, a line of outcrop about 30 miles 

 westward from that nearest in the anthracite fields, one finds a notable 

 decrease, for in western Wyoming county Doctor White gives but 300 feet 

 for entire thickness of the Mississippian,* and in Sullivan it appears to 

 be no greater. In Lycoming county, which lies on both sides of the 

 Allegheny crest, numerous measurements by Franklin Piatt and Andrew 

 Sherwood are available. In the northeast corner Mr Sherwood estimates 

 the Mississippian at 813 feet, of which he places 480 feet in the Pocono. 

 Mr Piatt, however, averages the interval for the same area at 730 feet, of 

 which he thinks 665 feet should be referred to the Pocono. Mr Piatt's 

 section is the more satisfactory, as the exposure is practicall}^ complete. 

 The rock is almost wholly current-bedded sandstone, and shows a one- 

 foot coal bed at 80 feet from the bottom. In northwestern Lj^coming 

 Mr Piatt finds, beginning at 120 feet below the Pottsville, gray current- 

 bedded sandstones 350 feet thick and resting on red shales and sand- 

 stones of the Catskill.f No conglomerate is reported in an}^ of the 

 Lycoming sections. The measurements in Bradford county are rather 

 indetinite, but Mr Piatt found in the Barcla}' coal field a greenish gray 

 current-bedded sandstone 300 feet thick, beginning at 110 feet below the 

 Pottsville. Professor Lesle3^ quoted by Mr Piatt, describes these rocks 

 as " gray flaggy sandstone " several hundred feet thick.]: No conglom- 

 erate appears in this county. It is evident that the lower transition 

 beds have practicall}^ disappeared. 



Doctor Chance's upper Pocono, in Clinton county, varies little from 

 400 feet, and consists of 60 to 80 per cent sandstone, the rest being sandy 

 shale. At 15 feet from the top is a layer 3 feet thick, composed of mixed 

 limestone and sandstone, but in no sense a conglomerate. The sand- 

 stone overlying it is rather coarse and gray. The sandstones, which for 

 the most part are hard, massive, fine grained, and show a foliated or 

 laminated structure, are made up of rounded grains and are usually 

 greenish gray. The lower layers are coarse, and some contain pebbles. § 

 Doctor Chance's lower Pocono represents the remnant of tlie disappear- 

 ing Catskill with the upper shales of the Chemung. For the most part 

 it appears to be equivalent to the shales overlying the first Venango oil 

 sand, which, according to the writer's classification, are Chemung. Mr 

 d'Invilliers gives as the generalized thickness of Pocono in Center county 

 625 feet, and reports the section as consisting along the Allegheny jilateau 



*I. C. White: G 7, p. 43. 



t Geology of Lj'coming and Sullivan counties (G 2), 1880. Andrew Sherwood, p. 10: Franklin 

 Piatt, pp. 10.}, 107, 127. 

 X Franklin Piatt: Rep. of Prog, in Bradford and Tioga counties (G), 1878, pp. 121, 127. 

 I H. M. Chance : Geology of Clinton county (G4), 1880, pp. 98, 125, 126. 



