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



of the Monongahela is 206, 250 and at the Ohio River 261 feet. 

 Beyond that river. 275, 300. 340 and 380 in Pennsylvania to just 

 beyond the Alonogahela River; 316 at a few miles farther and 212- 

 in the Frostburg basin of ^Maryland. Adding the coal beds and 

 their partings one has 213 at the western outcrop, 270 at the Ohio 

 River, 285 at western line of Pennsylvania, 400 near the Mononga- 

 hela, 370 beyond the Monongahela and 252 in the Frostburg basin of 

 Maryland.'- It is evident that the topographical conditions have 

 been changed and the area of deposit has become a trough with 

 its deepest line midway in the bituminous region. The ancient 

 trough of sedimentation at the east has disappeared. For in 

 another direction the contrast with the Athens conditions is equally 

 striking. No shortening of the section northward was observed in 

 the Athens, but in the ]\Ionongahela. the shortening in that direction- 

 is distinct. Many measurements are available in southwest Penn- 

 sylvania and West \^irginia.^^ These show that the thickness in- 

 creases from 156 feet at the most northerly exposure in Washington 

 county of Pennsylvania to about 400 feet at the West Virginia line,, 

 the increase being gradual. The extreme thickness is maintained in 

 West Virginia for more than 50 miles. Thence the section can be 

 followed only with difficulty as all horizons become indefinite, but 

 evidently it becomes shorter, for, where the horizons again become 

 definite, along the southern border, the thickness is 250 to 281 feet. 

 The conditions were similar during deposition of the Washington. 

 Throughout the Wheeling, the area of deposition was basin shaped,, 

 with the rate of subsidence increasing toward central West Vir- 

 ginia. It was contracting on all sides and there is little or nO' 

 reason to suppose that any important deposits were made in the 

 anthracite region or south from West Virginia. 



'"Ohio Geol. Surv., Vol. III., p. 262; Second Geol. Surv. Penn., Report 

 K, pp. 211, 216. 240, 340; "Carboniferous of the Appalachian Basin," BulL 

 Geol. Soc. Ainer., Vol. 18, 1907, p. 47; G. P. Grimsley, "Ohio, Brooke and' 

 Hancock Counties," West Virginia Geol. Surv., 1907, p. 39. 



"J. J. Stevenson, Second Geol. Surv. Penn., Rep. KKK, 1878, p. 292; 

 a considerable number of measurements cited here from Rep. K were made 

 by I. C. White; I. C. White, U. S. Survey, Bull. 65, pp. 54, 55; Well records- 

 in W. Va., Vol. I. 



