THE ALLEGHENY PLATEAU 16 



and witli a clearer conception of the relations. The statement of facts 

 is practically the same in both reports. 



No measurements are available for Clearfield and .Jefferson counties, 

 lying south from Elk and Forest, and nothing can be obtained until one 

 reaches the Conemaugh gaps through the Viaduct, Laurel, and Chestnut 

 hill, and the Youghiogheny gaps through the same anticlines farther 

 south. In the Conemaugh gap through Chestnut ridge, AVestmoreland 

 count}^ Stevenson found the Pocono a massive sandstone, 443 feet 

 thick, broken only by two shale beds, 3 and 10 feet respectively. Much 

 of it is current-bedded, and many layers, especially toward the bottom, 

 are conglomerate, with pebbles as large as a ])lum and often flat. A 

 4-inch bed of impure limestone was seen near the middle. The thick- 

 ness in the Youghiogheny gap through the same ridge is not far from 

 375 feet, the rock being mostly fine grained sandstone, though la3'ers of 

 conglomerate are numerous, as on the Conemaugh in the bottom 60 

 feet. In the Youghiogheny gap through Laurel ridge the thickness 

 appears to be not more than 300 feet.* The conglomerate layers with 

 small flat pebbles show a singular parallelism at exposures on both 

 rivers as well as at several localities on both sides of Chestnut ridge 

 along the National road in Fayette county. 



Doctor White records several sections in northern West Virginia. In 

 southeastern Preston count}^ along the Baltimore and Ohio railroad, 

 under the Viaduct axis of Pennsylvania — the Briery mountain of West 

 Virginia — he finds 566 feet of sandstones and shales with an impure 

 limestone, 1 foot thick, at 150 feet from the bottom, this possibly repre- 

 senting the thin limestone of the Conemaugh gap through Chestnut 

 ridge. The section is interesting as exhibiting a structure very familiar 

 in the oil-well records in the interior of the state. Somewhat condensed 

 it is 



Feet 



1. Sandstone 120 



2. Mostly shale 115 



3. Sandstone 75 



4. Shales, shaly sandstone, and sandstone 105 



5. Limestone, impure 1 



6. Mostly shale 150 



Number 2 contains 10 feet of sandstone, number 4, 12 feet of appar- 

 ently massive sandstone, and number 6, 18 feet, besides beds of shal}^ 

 sandstone and sandy shale.f The Laurel Hill anticline decreases south- 



*J. J. Stevenson: Report of progress in [the Fayette and Westmoreland district, part i, 1877. 

 (K 2), p. 291. The same, part ii (K 3), 1878, pp. 54, 77, 105. 

 tl. C. White : University of West Virginia Catalogue, 1882-83, p. 50. 



IV— Bull. Geol. Soc. Am., Vol. 14. 1902 



