ing to Mr. Carll. 

 170 J 



118 THE DEVONIAN AND CARBONIFEROUS. [bull. 80. 



Another table shows the difference between his interpretation and 

 that of Mr. Carll : 



m 



Feet. 



Horaewood Sandstone 30 ^j No. XII, according to Mr. Chance. 



Mercer group 30 | Feet. 



Connoquenessing group 155 }> 265 ^ 



Sharon group 10 1 I 435 f ee t No XII aerord- 



Sharon Conglomerate (Ohio Conglomerate)... 40 J y 6 ° x f®*' J^V n«rfi 



Sharon upper shales 30" 



Sharon upper sandstone 15 



Sharon middle shales 75 



Sharon lower sandstone 50^ 



Feet. 



Crawford upper (Cuyahoga) shales 135 



Berea grit (Third Mountain sand of oil men, Carll) 75 



Crawford lower (Bedford red) shales 



The last three members of this table, classed together, were called 

 li Crawford shale group" by J. P. Lesley. 1 



In the Report of Progress, G 4 , 2 Mr. H. Martin Chance published as 

 Part Second, " A Special Study of the Carboniferous and Devonian 

 strata along the West Branch of the Susquehanna River." 3 At the 

 time this report was written the Coal Measures series had been fairly 

 well studied, the Conglomerate as a base was established, and the eastern 

 section had been particularly well surveyed, classified, and compared 

 with that of Ohio. The northwestern sections of the State had been 

 examined and great difficulties had been found in identifying the vari- 

 ous members. 



Dr. Newberry, in the third volume of the Geology of Ohio, had re- 

 ported u that the Vespertine connects throughout this gap with the 

 Waverly, but the Umbral and Catskill do not reach Ohio." 



Mr. Chance says that — 



The Mauch Chunk red shale, No. XI, and the Red Catskill, No. IX, diminish in 

 thickness rapidly from the Alleghany Mountains westward, so that in a few miles the 

 latter entirely disappears ; whereas the Pocono (Vespertine, No. X) thins gradually 

 for a few miles, then maintains a nearly constant thickness for 90 miles, when it rap- 

 idly loses its lower half by a rise in the Chemung floor at the oil-sand shore line 

 and again stretches away to the west, with a nearly constant thickness, for 100 miles 

 or more. 



Among other causes productive of erroneous identifications in the northwestern 

 counties, insufficient paleontological data may be mentioned. The lines of demark- 

 ation between Subcarboniferous and Catskill and between Catskill and Chemung 

 fossil horizons are not uniformly drawn by paleontologists, and as — from the condi- 

 tions essential to the growth of shellfish — it seems certain that there must (at some 

 points) be an overlapping of the fossil fauna of one formation into that above it, the 

 structuralist can not accept unquestioningly an identification supported by paleon- 

 tological evidence alone. 



His correlations are well expressed in detail in a a Table showing the 



' I 4 . See foot-note, p. 224. 



2 Geol. Survey of Pennsylvania, Report on Clinton County, by H. M. Chance; including a description 

 of tbe Renovo coal basin, by C. A. Aahburner ; and notes on the Tangascootac coal basin, by F. Piatt, 

 pp. 183, 1880. 



3 Ibid., pp. 79-174. 



