178 BITUMENS AND PYROSCHISTS. [X. 



and are often, like coal, employed as valuable sources of volatile 

 hydrocarbons, although like it they contain little or no bitumen. 

 They may be regarded as clays or marls, holding, in a state of in- 

 timate admixture, a variable proportion of a matter approaching to 

 coal in its chemical characters. Although frequently dark brown or 

 black in color, they are sometimes light brown or even yellowish- 

 gray, as is the case with the Jurassic pyroschists of the department 

 of the Doubs, and those of tertiary age near Clerniont, both in France. 

 Remarkable examples of this are also given by Professor J. D. 

 Whitney in the pyroschists from the Utica formation in Iowa, 

 which were yellowish-brown, weathering to a bluish-ash color. 

 They, however, blackened when exposed to heat, burning with a 

 bright flame, and contained from eleven to twenty per cent of com- 

 bustible matter.* .... A pyroschist of the Utica formation, from 

 Collingwood on Lake Huron, examined by me, gave to dilute hydro- 

 chloric acid from fifty-three to fifty-eight per cent of carbonate of 

 lime, besides a little magnesia and oxide of iron. The insoluble 

 residue was snuff-brown in color, and, when heated, gave off a 

 bituminous odor. When ignited in a close vessel, it lost 12.6 per 

 cent of volatile and combustible matters, and left a coal-black resi- 

 due, which, by calcination in the open air, lost 8.4 per cent addi- 

 tional, making in all 21.0 per cent of volatile and carbonaceous 

 matters, and left an ash-gray argillaceous residue. This schist, 

 however, contained but a very small amount of bitumen ; for, on 

 treating the residue from a dilute acid with boiling benzole, tin-re 

 was dissolved about 1.0 per cent of a brown bituminous matter. 

 The residue, when heated, no longer evolved the odor of bitumen, 

 but rather one like burning lignite, and still gave, by ignition in 

 a close vessel, 11.8 per cent of volatile and inflammable matters. 

 When boiled with a solution of caustic soda, this was scarcely dis- 

 colored. In its insolubility, therefore, the organic matter of this 

 rock resembles true coal rather than lignite. Attempts have UTH 

 made, on a large scale, to distil this calcareous schist of Collinx- 

 wood, which was found to yield from 3.0 to 5.0 per cent of oily 

 and tarry matter, besides combustible gases and wakr. 



Overlying the Hamilton formation in Ontario are found Mn.-k 

 pyroschists, which are supposed to be the equivalent of the G< 

 slates of New York. A specimen of these from Bosanquet on Lake 



* For numerous analyses of pyroschists from this geological hori/on, 

 see a note appended to this paper in the American Journal of Science (2), 

 XXXV. 160. 



