480 STEVENSON— THE FORMATION OF COAL BEDS, [^'ov. i, 



with that under the Cambridge limestone and at others where it is 

 continuous with that above the Ames ; but it is notable throughout 

 its whole extent ; even at the northern border, where no other reds 

 are found in the Conemaugh, the Pittsburgh reds are from 30 to 50 

 feet thick. At the same time, it must be noted that this, like those 

 which precede and those which follow, is in no sense a uniform 

 deposit ; the variations in thickness and character are greater than 

 those of the sandstones and are marked by extreme irregularity. 

 IMaking all allowance for defective methods of keeping the records 

 of borings, one must recognize that a mass of red shale, 50 feet 

 thick in one well, may be replaced, even in the Central area, with 

 sandstone in another well only 200 feet away ; that red shales alter- 

 nate vertically with light gray, blue or almost white shales as well 

 as with gray white or bluish sandstones ; comparison of well records, 

 preserved and collated by I. C. White in the West Virginia reports, 

 leaves no room for doubt thafred shales are often continuous later- 

 ally with light colored shales and sandstones, and that the transition 

 may take place within a few rods. But in the upper portion, the 

 Pittsburgh reds are as nearly continuous throughout the whole area 

 as is any other deposit in the series. 



The Washington reds, the " Big reds " of the drillers, follow the 

 Ames limestone and, where that rock is absent, are often continuous 

 with the lower deposit. This mass spreads with considerable thick- 

 ness into counties adjoining the Central area but it underlies not 

 much more than 4,000 square miles and is absent at many places 

 even within the main red area. It seems to be wanting in most of 

 Ohio, but a thickness of 60 feet is reported in Muskingum county 

 at 50 miles from a locality on the Ohio River, where it is said to be 

 100 feet thick, no reds having been observed in the intervening space. 

 It occurs as red shale occasionally in northern West Virginia but 

 seems to be wanting in Pennsylvania, though its place is marked by 

 the fine-grained Birmingham shale of that state. Its variations later- 

 ally and vertically are wholly like those of the Pittsburgh. The area 

 of red shows more notable contraction in the upper part of the Cone- 

 maugh, but, locally, the reds were deposited in an area almost as 

 great as that of the Pittsburgh. Thick deposits are reported from 

 some counties within the Central area and none whatever from 



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