hy Dr, T. Sterry Hunt. 243 



tertiary formation (of upper miocene or lower pliocene age,) which 

 consist of limestones, sandstones and shales, associated with beds of 

 lignite. The bitumen is found not only in the famous pitch lake, but 

 in situ,wh.ere it is confined to particular strata which were originally 

 shales containing vegetable remains ; these have undergone '' a 

 special mineralization producing a bituminous matter instead of coal 

 or lignite. This operation is not attributable to heat, nor of the na- 

 ture of a distillation, but is due to chemical reactions at the ordi- 

 nary temperature, and under the normal conditions of climate." 

 He also describes wood partially converted into bitumen, which 

 last when removed by solution leaves a portion of woody 

 tissue. (Proc. Geol. Soc. London, May, 1860.) 



The sources of petroleum and mineral pitch in Europe and in 

 Asia, are for the most part, like those just named, confined to rocks 

 of newer secondary and tertiary age, though they are not wanting 

 in the palaeozoic strata, which in Canada and the United States 

 furnish such abundant supplies of petroleum. In the great palae- 

 ozoic basin of North America bitumen, either in a liquid or solid 

 state, is found in the strata at several different horizons. The 

 forms in which it now occurs depend in great measure upon 

 the presence or absence of atmospheric oxygen, since by oxy- 

 dation and volatilization the naphtha or petroleum, as we have 

 already explained, becomes slowly changed into asphalt or 

 mineral pitch, which is solid at ordinary temperature. It 

 would even appear that by a continuance of the same action 

 the bitumen may lose its fusibility and solubility, and became con- 

 verted into a coal-like matter. Thus in the Calciferous sandrock 

 in New York a black substance, which has beenjcalled anthracite, 

 occurs in cavities with crystals of bitter spar and quartz. It some- 

 times coats these crystals or the walls of the cavities, and at other 

 times appears in the form of buttons or drops, evidently according 

 to Mr. Vanuxem, having been introduced into these cavities in a 

 liquid state, and subsequently hardened as a layer above the crys- 

 tals, which have conformed to them, showing that this coal-like 

 matter was once in a plastic state. It is very pulverulent, 

 brittle, of a shining black, and according to Vanuxem yielded 

 but little ash, and 11^ per cent of volatile matter, which he 

 regarded as water, (Vanuxem, Geology of New York, iii. 33). 

 A similar material occurs in the Quebec group in Canada, 

 the equivalent of the Calciferous sand-rock, and fills cavities 

 and fissures in the limestones, sandstones, and even in the accom- 



