30 DESCRIPTIONS OF MINERALS. 



Tlie following are average results, from many analyses : 



Pennsylvania anthracites... ■ 



Pennsylvania semi-antlira- 

 eites 



Pennsylvania semi-bitumi- 

 nous 



Maryland semi-bituminous. . 



Pennsylvania bituminous. .. 



Virginia bituminous 



Ohio bituminous 



Indiana bituminous 



Illinois bituminous 



Iowa bituminous 



Xos. 



10 



11 



142 



128 



50 



Vol. Fixed 



c m- Car- Ash. 



bust. bon. I 



1-59-1 -61 

 1-39-1 -GO 



1-30-1 -41 



1-30-143 



1 29-1 -43 



1-24-1-47 

 1-19-F41 

 1-21-1-35 



3-92 

 5 -70 



16-85 



S9-77 

 88-23 



8286 



72-95 



j 15 50 7 



2S-.35 

 29-88 

 3V24 

 43-20 



3190 



65-18 



59-06 ! 



60-26 



53-47 



62-44 



43-02 



6-31 

 .607 



7-16 

 10-20 



10-47 



6-47 

 11 "06 I 

 4-50 1 



3 33 

 5-66 i 



Analysis. 



Johnson. 

 Geol. Survey. 



Geol. Survey. 



Johnson. 



( Johnson and 

 "( Geol. Survey. 



Johnson. 



Johnson. 



Wormley. 



Cox. 



Blaney. 



Emery. 



The ordinary impurities of coal, making up its ash, arc silica, a 

 little potash and soda, and sometimes alumina, with often oxide of 

 iron, derived usually from sulphide of iron ; besides, in the less pure 

 kinds, more or less clay or shale. The amount of ash does not ordina- 

 rily exceed 6 per cent.* but it is sometimes 30 per cent. ; and rarely it 

 is less than 2 per cent. When not over 3 or 4 per cent, the whole may 

 have come from the plants which contributed the most of the material 

 of the coal, since the Lycopods have much alumina in the ash, and 

 the Equiseta much silica. 



There is present in most coal traces of sulphide of iron (pyrite\ suf- 

 ficient to give sulphur fumes to the gases from the burning coal, and 

 sometimes enough to make the coal valueless in metallurgical opera- 

 tions. Some thin layers are occasionally full of concretionary pyrite. 

 The sulphur was derived from the plants or from "animal life in the 

 waters. Sulphur also occurs, in some coal beds, as a constituent of a 

 resinous substance ; and Wormley has shown that part of the sulphur 

 in the Ohio coals is in some analogous state, there being not iron 

 enough present to take the whole into combination. 



The average amount of ash in eighty-eight coals from the southern 

 half of Ohio, according to Wormley, is 4-?lS per cent.; in sixty-six 

 coals from the northern half, 5*120 ; in all, from both regions, 4891 ; 

 or, omitting ten, having more than ten per cent, of ash, the average is 

 4 "28. In eleven Ohio cannels, the average amount of ash was 12 827. 

 The moisture in the Ohio coals, according to the analyses of Wormley, 

 varies from 1-10 to 9 10 per cent, of the coal. 



Mineral coal occurs in extensive beds or layers, interstratified with 

 different rock strata. The associate rocks are usually clay shales (or 

 slaty beds) and sandstones ; and the sandstones are occasionally coarse 

 grit rocks or conglomerates. There are sometimes also beds of lime- 

 stone alternating" with the other deposits. 



Coal-beds vary in thickness from a fraction of an inch to 40 feet. 

 The thickness of a bed may increase or diminish much in the course 

 of a few miles, or the coal may become too shaly to work. 



