502 STEVENSON— THE FORMATION OF COAL BEDS. [Nov. i, 



tions are with the eastern side. The most easterly point in Penn- 

 sylvania, at which the Cambridge can be recognized with certainty, 

 is almost 60 miles east from the Ohio line and about 70 miles north 

 from that of West Virginia. Thence it is persistent into Ohio. 

 The direction of the area is almost westward in Pennsylvania but in 

 Ohio it becomes west of south, and the bed is easily followed across 

 that state and Kentucky to the last exposure of its horizon. In 

 southern Ohio and in Kentucky it extends eastward beyond any 

 predecessor and at the south it reaches into West Virginia ; but it is 

 absent under the Wirt anticline in both Ohio and West Virginia. 

 In Pennsylvania, its area is far less than that of the Vanport and 

 the thickness rarely attains 8 feet. The distribution of the deposit 

 indicates a return to the earlier condition, as this is confined to the 

 west side. The abundant fauna is marine.^^ 



Midway in the Conemaugh is the remarkable deposit, the Ames 

 limestone of E. B. Andrews, the Green Fossiliferous limestone of 

 the early Pennsylvania reports. It overlies the Pittsburgh reds, 

 from which it is separated in extensive areas by the Harlem coal bed 

 and the associated shales. It has not been discovered anywhere 

 east from the Allegheny Mountains unless one accept as its equiva- 

 lent the A-Iill Creek limestone of the Northern Anthracite field, 

 which certainly is in the Conemaugh, possibly not far from the 

 Ames horizon. The Ames is thin, seldom more than 4 feet, and is 

 more or less argillaceous, especially on the eastern side. The color 

 is bluish green, thoroughly characteristic in most of the area, so 

 that the bed is a most important stratigraphic guide. Along the 

 eastern border it has been recognized positively to 75 miles south 

 from the Pennsylvania line ; it is present in western Maryland and 

 southwestern Pennsylvania, wherever its horizon is exposed ; it is 

 equally persistent in Ohio and Kentucky, being the Fourth Fossil- 

 iferous limestone in the latter state. It extends on the west side 

 to the middle line of the basin, being exposed under the Wirt anti- 

 cline in both Ohio and West Virginia. It was deposited in an area 



^'For observations by Martin, I. C. White, W. G. Piatt, Stevenson, 

 Ortofi, Andrews, Lovejoy and Bownocker, see " Carboniferous," etc., as 

 above, pp. 168, 175-180, 183-194, 197-201. 



