I9I2.] STEVENSON— THE FORMATION OF COAL BEDS. 443 



maugh and had lifted much of the region above the area of deposi- 

 tion. On the latter fold, a deep railway cutting shows sandstone, 

 25 feet thick, resting on shales with limestone. At a few rods west, 

 the sandstone suddenly becomes 75 feet thick, replacing the under- 

 lying beds ; but, within two miles, the lower part of the sandstone 

 disappears almost abruptly and the normal section reappears. The 

 same sandstone was seen in another section farther north, but, in 

 that direction, the horizon soon passes into the air while south- 

 wardly it passes almost at once under cover. The rocks on each 

 side of this valley have a dip of 80 feet per mile, whereas that of 

 the sandstone within is but 40 feet. The crest of the Washington 

 axis is shown well in a railway cutting. There, the shales overlying 

 the Ames limestone, midway in the Conemaugh, come down and 

 replace that limestone and underlying beds to an unknown distance 

 below the roadway ; but at barely half a mile the normal section is 

 reached. This is clearly on the crest of the fold, for the Ames 

 limestone dips in opposite directions on the sides of the shale-filled 

 space. On the west slope of the Salzburg anticline in Westmore- 

 land county, near Penn station, one may see an illustration of alter- 

 nating erosion and deposition, in type resembling the " Symon 

 Fault." This is in the Monongahela formation, somewhat more 

 than 100 feet from the bottom. At the entrance to a long railway 

 cutting, a sandstone, 60 feet thick, rests on 6 feet of irregular sand- 

 stone, containing streaks of coal. Within a few yards, 8 feet of 

 limestone is shown under the upper sandstone but it continues for 

 less than 20 yards and is cut off abruptly by the sandstone. In a 

 branch cutting, the sandstone is well exposed for a short distance 

 but is soon replaced with yellow shale, which is very local. 



Aside from the continued contraction of the area of deposition, 

 there is little evidence of great movements within the Appalachian 

 basin. For considerable periods of time, areas of many hundreds 

 of square miles received no deposits; the anticlines evidently were 

 developed slowly. The Appalachian revolution apparently spent 

 its force during Coall Measures time mostly at the east. But in 

 Europe the Upper Carboniferous disturbances have left more note- 



