1869.] ROCKS CONTAINING ORGANIC SUBSTANCES. +55 



not wonder if such bituminous mixures of mica and feldspar, 

 or bituminous mica-schist, were found to be abundant in ahnost 

 all our districts of crystalline rocks. When the carbonaceous 

 substance becomes more predominant, the silver-white colour 

 passes into daik brown, and this colour totally prevails in the 

 variety b, which at a superficial glance seems to be a quite 

 homogeneous, black or dark brown substance. A closer exam- 

 ination, however, shows, that this colour comes from innumer- 

 able small black, well defined grains immixed in the greyish 

 orthoclase. Some scales of mica, of the same aspect as the mica 

 in the schistose variety, and small grains of calcite, may also be 

 discovered. Occasionally the felspar and calcite are concentrated 

 into somewhat larger white nodules, free from the black mineral. — 

 If the variety b — (b contains less of bitumen) — is heated in the 

 air or in oxygen, the carbonaceous substance is destroyed, and 

 the blackish colour changes into greyish-white. Before the piece 

 is red-hot, a combustible gas is given off, enveloping the heated 

 mineral in a flame, resembling the flame of burning hydrogen. 

 Even when heated in a retort the rock gives much gas, in this 

 respect quite resembling bituminous coal. With boiling alkali a 

 dark brown solution is obiained, which gives witli muriatic acid 

 a brown flocculent precipitate. 



The carbonaceous substance is very brittle, and the rock is 

 therefore more friable than common gneiss, not more, however, 

 than might be presumed ol a gneiss penetrated with cavities of 

 the form and volume of the immixed coaly particles. But near 

 the surface the rock is already much decomposed, and so brittle 

 that large pieces may be crumbled with a few blows. The grains 

 of orthoclase, both in the altered and unaltered rock, break along 

 the cleavages of the felspar, and the fracture of the rock is thus 

 crystaline. Accordingly we have here not to do with a sandstone, 

 but with a rock, probably originated by the solidification and 

 crystallization of a claylike sediment, consisting of organic sub- 

 stances and inorganic matter, of the same constituents as the 

 common felspar. That a change in the relative position of the 

 atoms, i.e., a cry?tallisation in a solid mass tending to a disposition 

 of its molecules according to the best conditions of equilibrium, 

 did take place, without the aid of water or heat, during the 

 immense time that has elapsed since the gneiss period, seems not 

 at all improbable, when we consider, that such a change often 

 takes place, for instance in the axis of a locomotive in the course 



