1912] STEVENSON— THE FORMATION OF COAL BEDS. 477 



with coal beds ; it is necessary here to study in detail only the red 

 shales and to note a few matters concerning shale deposits generally. 

 Tlic Red Shales. — The red and green muds and laminated sand- 

 stones of the Catskill pass gradually into the early Carboniferous 

 in a great area within Pennsylvania and Virginia. In like manner, 

 the red shales of the Upper Mississippian pass into the Pottsville 

 through a transition series of sandstones, conglomerates and red to 

 green shale beds, this feature being especially characteristic in the 

 southern anthracite field, where the column is complete. The reds 

 and greens of the Catskill mark a condition, which originated in 

 southeastern New York during the Middle Devonian and spread 

 slowly west and southwest, reaching southwestern Pennsylvania late 

 in the Chemung, the last great division of th€ Devonian. The con- 

 dition, whatever its cause may have been, appears to have been with- 

 out relation to the character of the water; the fauna in the northern 

 portion of the area is freshwater, but in southwestern Virginia,^^ 

 very near the termination of the red deposits, Spirifer disjunctus 

 and some other forms were obtained at the top of the formation, 

 showing that marine conditions reached as far northward as New 

 River and that they were not inconsistent with the deposition of red 

 beds. The Mauch Chunk or Upper Mississippian red beds seem to 

 have yielded no marine forms in eastern Pennsylvania, but in south- 

 ern Pennsylvania and southward, the middle and lower portions are 

 gradually replaced with the Maxville limestone, which is marine, 

 while in western Pennsylvania the upper portion or Shenango shale 

 has yielded marine forms in Crawford, Mercer and Fayette coun- 

 ties. ^^ The fossils are large and they did not live amid unfavorable 

 conditions. The shales are red in Fayette county, so that again it is 

 evident that influx of salt water did not prevent formation of red 

 beds. The Pennsylvanian red shales have neither the constancy nor 

 the extent of those in the Catskill and Mauch Chunk, but they resem- 

 ble the former in that the conditions favoring their formation existed 

 at first in a small area, whence they gradually spread ; they differ 



"J. J. Stevenson, "The Chemung and Catskill on the Eastern Side of 

 the Appalachian Basin," Proc. A. A. A. S., Vol. XL., 1891, separate, p. 7. 



■'L C. White, Sec. Geol. Surv. Penn., Rep. Q4, 1881, p. 77; J. J. Steven- 

 son, ibid.. Rep. KKK, 1878, p. 308. 



