APPLICATION OF WRITER S HYPOTHESIS. 67 



far southwestward — that is, along the strike — as does the Southern. The 

 thickness of coal varies from 52 to 53 feet in the eastern Middle, and .from 

 58 to 40 feet in the western Middle, the last thickness being near 

 Shamokin at the westerly end;* but in both the Southern and the 

 Middle the Mammoth bed alone sometimes shows more than 100 feet of 

 clear coal.f The Northern field in the westerly portion shows from 44 to 

 53 feet. The anthracite region, then, except in the extreme southerly 

 prongs of the Southern field, shows an average thickness of from 40 to 60 

 feet of coal, the greater thickness being at the northeast. 



Going southward or, better, along the trend, in this anthracite strip, 

 the remarkable diminution in thickness noticed in the Southern field is 

 found to be not local, for in Broad Top the thickness of coal does not 

 exceed 14 or 15 feet,'| and Professor White found the thickness on the 

 east side of the Cumberland basin in West Virginia to be not more than 

 15 feet, with at least 2 feet of slate. § 



In passing from the anthracite strip to the bituminous basins one 

 finds no prong, like that of the Southern field, to show the continuous 

 decrease in thickness ; but that is not needed, for the decrease is suffi- 

 ciently marked. In the first bituminous basin the thickness of the beds 

 of the lower coal group, including all slates and partings, varies from 21 to 

 23 feet, the greater thickness being at the north ; in the second basin the 

 extreme is 19 feet near the ^Earyland line and 22 feet in Indiana county, 

 while in the third basin and beyond, the thickness decreases until at the 

 Ohio line it varies (all slates and partings being included) from 8 feet 6 

 inches to 13 feet 4 inches.] | 



The lower barren group shows almost equally striking variations, for 

 in the Southern field the interval between coal-beds E and H contains 

 from 25 to 36 feet of coal, partings not included ; the western Middle 

 shows 39 feet at the eastern end and 20 at the western end, while in the 

 Northern field this interval has from 17 to 27 feet. The Broad Top field 

 shows not more than 5 feet. No detailed measurement was made by 

 Professor White, owing to lack of exposures, on the east side of the Cum- 

 berland basin. Elsewhere in Pennsylvania and Ohio the amount of 

 coal in this interval is extremely uncertain, the average in any single 

 section seldom being more than 4 or 5 feet, though occasionally, as in 

 Guernsey county of Ohio and Somerset county of Pennsylvania, a bed 



* Ashburner : Annual Report for 1885, pp. 339, 341. 349, 351. 

 t Ashburner: First Report on Anthracite Coal-field, pp. 95, 103, 231, 232. 

 J Stevenson: Geol. of Bedford and Fulton Counties, 1882, pp. 60, 235, 259. 

 gl. C. White: Proe. Amer. Phil. Society, vol. xix, pp. 440-441. 



11 These measurements are taken from the reports of the Second Geol. Surv. of Penn-sylvania by 

 White, Piatt and Stevenson. 



