314 PALEOZOIC TIME. 



ing to Rogers, into West Virginia and Ohio, over an area at least two 

 hundred and twenty-five miles by one hundred ; and into Kentucky, 

 according to Lesquereux. It varies in thickness, being twelve to 

 sixteen feet in the Cumberland basin, six feet at Wheeling, four to- 

 eight feet in Athens County, Ohio, four feet two inches at Pomeroy, 

 where it is the " Pomeroy " bed, six and one-half to nine and one-half 

 feet in West Virginia, at Morgantown, and farther south, on the 

 Guyandotte, two to three feet. 



At Pictou, in Nova Scotia, one of the coal-beds has the extra- 

 ordinary thickness of thirty-eight feet, and a second fifteen and one- 

 half feet. 



A bed of coal, even when purest, consists of distinct layers. The 

 layers are not usually separable, unless the coal is quite impure from 

 the presence of clay ; but they are still distinct in alternating shades 

 of black, and may be seen in almost any hand specimen of the hard- 

 est anthracite, forming a delicate, though faint, banding of the coal. 



In some of the bituminous coal of the Interior basin, a cross-fracture 

 shows it to be made up of alternate laminae of black, shining, compact 

 bituminous coal, and a soft, pulverulent carbonaceous matter, looking 

 much like common charcoal. 



The Coal-measures, from the bottom (No. 1) to No. 15, in the pre- 

 ceding section, are sometimes designated the Lower Coal-measures^ 

 Of the rest, or Upper division, Nos. 16 to 33 are called the Barren 

 Measures. 



3. Kinds of Mineral Goal. — The Mineral Coals, setting aside im- 

 purities, are essentially compounds of carbon (the fundamental ele- 

 ment of charcoal), hydrogen, and oxygen. The carbon varies from 

 75 to 93 per cent., or, impurities excluded, — which constitute usually 

 2 to 10 per cent., — from 77 to 98 per cent. The most of them yield, 

 when highly heated, mineral oil or mineral tar, along with some in- 

 flammable gas ; and it is owing to this that they burn with a bright 

 yellow flame. The oil, like the most of the gas, consists of carbon 

 and hydrogen. The coals, like the black carbonaceous shales mentioned 

 on page 268, do not contain mineral oil, any more than hydrocarbon 

 gas, as is shown on treatment with the solvents of mineral oils. The 

 oil is a product, and not an educt. Since such oils, tars, and gas burn 

 like bitumen, and with similar odor, coals of this kind are said to be 

 bituminous, although actually containing no bitumen, and also yielding 

 none, — bitumen being mainly an oxygenated hydrocarbon, and thus 

 differing from mineral oil. Coals also contain traces of nitrogen; 

 they afford generally 3 to 5 per cent., or more, of moisture, which is 

 driven off at a temperature of 250° F. 



The following are the characters of the kinds of Carboniferous 

 mineral coals : — 



