CONSTITUENT MINERALS OF ROCKS. 



69 



The composition of mineral coal varies much. The following are the results 



of some analyses : — 



Volatile 

 combustible Fixed 



matter. carbon. Ash. 



Anthracites of Pennsylvania 3.84 87.45 7.37 = 98.66 Johnson. 



Bituminous, Pittsburg 32.95 64.72 2.31= 99.98 Johnson. 



La Salle, Illinois 39.17 54.19 6.64 = 100 Whitney. 



Cannel, Boghead, Scotland 66.35 30.88 2.77 = 100 Silliman. 



" Breckenridge co., Kentucky 55.7-71.7 28.3-44.3 7.-12.30 Peter. 



" Wigan, Lancashire,England 50.18 46.42 3.40 = 100 Heddle. 



Asphaltic coal 61.74 36.04 2.22 = 100 Silliman. 



Ultimate analyses, to determine the proportions of the elements, have given — 

 the ashes excluded — 



Hydrogen. Oxygen. Nitrogen. 



1.75 4.20 0.00 Kegnault. 



5.5 12.3 0.00 Bischof. 



11.24 6.73 0.87 Peter. 



7.84 7.05 2.75 Peter. 



9.14 8.19 Wetherill. 



5.3 22.4 Regnault. 



6.1 33.8 Vaux. 



4.1 15.2 Baer. 



Carbon 



Anthracite 94.05 



Bituminous 82.2 



Cannel, Boghead 80.49 



Cannel, Breckenridge ... 82.36 



Asphaltic coal 82.67 



Lignite 72.3 



Peat, Provincetown 60.1 



Peat coal, Westphalia... 80.7 



The ashes consist mostly of silica and alumina, in the ratio of 1 of the former 

 to 1 or 2 of the latter, with a trace of lime and magnesia; and, in those coals 

 which afford a red ash, some oxyd of iron, often derived from pyrites mixed 

 with the coal. In good coals, the ash does not exceed 10 per cent., of which, as 

 an average, 2 to 4 might be silica, 4 to 7 alumina, and ^ each lime and magnesia, 

 or oxyd of iron. 



Resins of several kinds occur in some coal-beds, especially in those of tertiary 

 age. Amber is of this kind. They come from the ancient trees, but have been 

 altered in the course of their long burial. 



Fossils. — From the above account of the composition of the hard 

 parts of organic beings, their influence on the composition of rocks 

 is readily inferred. 



But the fossils themselves seldom retain completely, even in the 

 case of such stony secretions as shells and corals, their original 

 constitution. There is usually a loss of the organic matter. There 

 is often a further change of the carbonate of lime into a new mole- 

 cular condition, manifest in the fact that the fossil has the oblique 

 cleavage of calcite : and in this change there is a loss of part or all 

 of the phosphate or fluorid. There is sometimes, again, a change to 

 dolomite, in which the carbonate of lime becomes a carbonate of 

 lime and magnesia. In other cases, of very common occurrence, all 

 the fossils of a rock, whether limestone or sandstone, are changed 



