22 J.. T.STEVENSON — LOWER CARBONIFEROUS, APPALACHIAN BASIX 



and he regards the upper 70 feet as unquestionably Mauch Chunk.* 

 Some of the lower portion is Chemung, but that is unimportant here, as 

 the thickness suffices to show the rapid decrease westward along the 

 northern outcrop in Pennsylvania. In Potter county is found the most 

 easterly line at which Doctor White's Shenango sandstone, the sub- 

 Olean conglomerate of other authors, has been recognized fully ; but the 

 reader who has followed these notes can have no difficult}^ in finding 

 traces of it along the northern outcrop in the persistent sandstone, often 

 conglomerate at the top of the Pocono, w^iich is so characteristic that 

 Doctor White when he reached the northeastern outcrop was almost 

 read}^ at once to identify it with his Shenango. f From Potter westward 

 its pebbles are flat like those of the persistent Chemung conglomerates, 

 but it becomes conglomerate westward. In Clinton county it is only 

 coarse, while in Cameron (west from Clinton) and in western Potter, at 

 the north, it is conglomerate. 



McKean county adjoins Potter at the west. There Mr Ashburner finds 

 this Shenango sandstone, 40 feet thick, sometimes largel}" conglomerate, 

 at others largely hard, massive, finegrained ferruginous sandstone. His 

 lower Pocono, which is the lower portion of Doctor Chance's upper 

 Pocono, is said to be 150 to 190 feet thick, extending downward to the 

 Marvin Creek Limestone, which contains Chemung fossils. This may be 

 the persistent limestone already referred to as found in Tioga county. 

 Mr Ashburner regards it as equivalent to that occurring at the same 

 horizon in Elk county (south from McKean) and to Doctor White's 

 lower Meadville limestone of Crawford county. J 



In Cameron count.y (south from McKean and west from Clinton) Mr 

 Ashburner finds the Pocono varying from 745 feet in the extreme middle 

 east to 470 feet in the extreme northeast, but for the most part the sec- 

 tions are too imperfect to justify definite conclusions respecting either 

 thickness or boundaries. It is sufficiently clear, however, that at 50 

 to 60 feet below the Pottsville sandstones begin, and that some of 

 them are coarsely conglomerate. Fragments of the Shenango sandstone 

 (sub-Olean) occur in northern Elk, west from Cameron. A fossiliferous 

 limestone occurs at 200 feet below the Pottsville. For this county the 

 Pocono is given as from 500 to 610 feet, including some fossiliferous 

 limestones.§ The discrepancies between the descriptions by Mr Ash- 

 burner and those by Doctor Chance in G 4 are apparent rather than 

 real. Doctor Chance has presented the conditions more methodically 



*C. A. Asliburner : Geology of Potter county (Ga), 1880, p. 104. 



tl. C. White: G5, p. 6G. 



X G. A. Ashburner : Geology of McKean county (R), 1880, pp. 64-69. 



§ C. A. Ashburner : The township geology of Elk and Forest counties (R 2), 18SJ, pp. 18, 19, 105, 247. 



