GENERAL DESCRIPTION OF THE MAUCH CHUNK FORMATION 451 



which rise on each side to a height in the neighborhood of a tliousand feet. 



The broader characters and relations of the Mauch Chimin shales of 

 Pennsylvania and the synchronous deposits of other portions of the Ap- 

 palachian basin have been recently so admirably summed np by J. J. 

 Stevenson* from the previous studies of himself and others that only 

 sufficient need be here outlined to bring the chief features to mind. 



The formation in question was laid down with a character, thickness, 

 and distribution much more variable than that of the underlying Pocono. 

 Its maximum development occurs in the anthracite coal regions and it 

 there possesses its typical character. Beyond the limits of the state of 

 Pennsylvania the equivalent formations are so different that other names 

 must be applied. In eastern Ohio the strata pass into the upper part 

 of the Waverly group, while to the southwest in Maryland and Virginia 

 the Greenbrier limestone occupies the horizon of the lower portion of 

 the shales. In contrast to the considerable thickness to the south, the 

 shales are thin along all the northern outcrops in Pennsylvania and 

 often missing from between the Pocono below and the Pottsville above. 



The Mauch Chunk reaches its greatest thickness in the region of the 

 southern anthracite coal field, according to Rogers measuring at least 

 3,000 feet at Pottsville. At Mauch Chunk, Winslow gives figures of 

 2,168 feet on the south side of the syncline and 3,-342 on the north. 

 From these maximum thicknesses it diminishes northward to 1,000 feet 

 at Solomons gap, near Wilkes Barre, and 150 feet of green shales and 

 flaggy sandstones at Pittston. Passing westward from Pottsville, first 

 to the Broad Top coal field, Ashburner and Billin give it a thickness of 

 1,100 feet, divided into: 1, Upper shales and sandstones, 910 feet; 2, 

 Mountain (Greenbrier) limestone, 49 feet; 3, Lower shales and sand- 

 stones, 141 feet.f Northwest of the Broad Top field and back of the 

 Alleghany Mountain front the thickness is given by Butts, in the Ebens- 

 burg, Pennsylvania, folio, as but 180 feet, of which the lower 80 feet 

 consist of thick bedded gray to greenish sandstone, corresponding per- 

 haps to the Greenbrier limestone, and underlaid by 5 to 6 feet of inter- 

 bedded red shale and sandstone. At the most southwestern outcrop in 

 Pennsylvania, that of Laurel ridge ( Masontown-TJniontown quadrangle), 

 M. R. Campbell gives the entire thickness as 250 feet, consisting of three 

 members. At the base are 50 feet of typical Mauch Chunk red shale, 

 followed by 30 feet of Greenbrier limestone, which is in turn succeeded 

 by 170 feet of red and green shales, with occasional beds of greenish 

 sandstone. 



* Lower Carboniferous of the Appalachian basin. Bull. Geol. Soc. Am., vol. 14, 1902, 

 pp. 16-96. 



t Second Geological Survey of Pennsylvania. Summary, final report, vol. 3, part 1, 

 p. 1833. 



