1892.] NATURAL SCIENCES OF PHILADELPHIA. 85 



the coal measures proper, excluding the lower or Millstone grit 

 section (generally known in Pennsylvania simply as "the con- 

 glomerate"), have an aggregate thickness "varying from 100 to 

 1000 feet in the Interior coal areas, to 4000 feet where greatest in 

 Pennsylvania, and over 8000 feet in Nova Scotia.t 



The general tendencv both of the measures and the interstratified 

 coal seams, is to thin ofl'from N. E. to S. W. across the entire terri- 

 tory of the United States, the lower or largest beds gradually dis- 

 appearing, until in Texas only the top or latest member of the 

 series is present, showing both at the Gordon and the Strawn mines, 

 a maximum thickness of but twenty-two inches. General sections 

 everywhere show thick beds of conglomerates, sand and sometimes 

 limestones, and slaty shales with comjoaratively thin seams of coal. 

 An extremely favorable section from Western Pennsylvania, taken 

 from Lesley by the last quoted authority, shows in 810 feet of aggregate 

 thickness, a total thickness of coal amounting to 25 feet in eight seams 

 or beds, of which but two, one of six, the other of eight feet, are 

 workable. While every proportion exists between the thickness of 

 the measures and that of the contained coal, as well as betw'een the 

 coal seams themselves, the above is a fairly illustrative section from 

 the best carboniferous field in the United States except the anthra- 

 cite, which in the most valuable portions of the field probably 

 averages a greater richness. The coal seams themselves though fre- 

 quently extending continuously and perfectly identified for miles, 

 vary in thickness from an extreme maximum of thirty feet to noth- 

 ing, even the largest often thinning out over long distances to a 

 meagre layer of carboniferous slate or dirt. In the Lykens Valley 

 Coal Company's operations, for instance, in the lower or Lykens bed 

 at Short Mountain, an extensive and hitherto reliable seam of ten 

 feet, suddenly " pinched " out to such a trace, and was followed 

 through the rock at heavy cost of time and money for over 6000 

 feet, before it resumed sufficient thickness for mining. These exces- 

 sive and sudden eccentricities in thickness and value, though occur- 

 ring to some extent throughout all the coal fields, abound especially 

 in the anthracite district of Pennsylvania, that being eminently the 

 region of contortions, faults, foldings and disturbances, which in fact 

 accompanied or caused the metamorphism by which coal of ordinary 

 volatility, was refined into anthracite. The general continuity and 

 identity of coal seams, accompanied by frequent changes in thick- 

 t Ibid. pp. 3U9. 



