I9I2.J STEVENSON— THE FORMATION OF COAL BEDS. 503 



of not less than 16,000 miles, possibly much more, since no informa- 

 tion can be derived from the ordinary well records. This widely 

 extended deposit was certainly not continuous with the Mill Creek 

 limestone of the Northern field; the nearest outcrops of the two 

 rocks are separated by 150 miles, including a part of the bituminous 

 region in which the Ames never existed. The fauna is marine 

 throughout, even on the extreme western border in Meigs county of 

 Ohio where Condit^*^ found the limestone impure, sandy, ferrugi- 

 nous, conglomeratic with pebbles of sandstone and with sun cracks 

 on its upper surface. This marine invasion, affecting the greater 

 part of the Conemaugh area, followed the deposition of the fine 

 muds known as the Pittsburgh reds and was succeeded by the 

 Washington reds. Even where the reds are absent, the limestone is 

 usually between deposits of fine grain. Marine conditions preceded 

 it and continued after it; shales equivalent to the Pittsburgh reds 

 carry a marine fauna at some localities and, in Pennsylvania, 

 marine forms persisted up to 50 feet above the limestone. ^^ 



The only limestones in the anthracite region are in the northern 

 field, where they were seen by Ashburner. Three of them are 

 without fossils but the fourth, the Mill Creek at 688 feet above the 

 Baltimore coal bed and one foot thick, has a marine fauna. A 

 black shale at Dundee, in the same field and 250 feet above the 

 limestone, has the same assemblage of fossils. A peculiar feature 

 of this fauna is that it includes some forms unknown elsewhere in 

 the Appalachian basin, though abundant in the coal area beyond 

 Cincinnatia — which seems to indicate communication by some other 

 way than that at the southwest. 



Marine invasions practically ceased with the Ames episode: 

 there are other beds of limestone in the upper part of the Cone- 

 maugh but they appear to be at least non-marine. 



Five limestones have been recognized in the Monongahela, but 

 they are confined to a small space in southwestern Pennsylvania and 



'"D. D. Condit, letter of April 24, 1912. The locality is Sec. 10, Salem 

 township, Meigs county. 



" The observations by I. C. White, Stevenson, W. G. Piatt, Martin, 

 Newberry. Hodge and Andrews are recorded in "Carboniferous," etc., as 

 above, pp. 167-202, 208, 211, 215. 



PROC. AMER. PHIL. SOC, LI. 207 F, PRINTED DEC. 16, I9I2. 



