320 HISTORY OF PETROLEUM OR ROCK OIL. 



eludes more or less completely that of the other, and that bitumen 

 has been generated under conditions different from those which have 

 transformed organic matters into coal and lignite, and probably in deep 

 water deposits, from which atmospheric oxygen was excluded. Thus 

 in the palaeozoic strata of North America we find in the Utica and 

 Hamilton formations highly inflammable pyroschists, which contain 

 no soluble bitumen, and the same is true to a certain extent of some 

 limestones, while the Trenton and Corniferous limestones of the same 

 series are impregnated with petroleum or mineral pitch, and, as we 

 shall show, give rise to petroleum springs. The fact that interme- 

 diate porous strata of similar mineral characters are destitute of bitu- 

 men, shows that this material cannot have been derived from overly- 

 ing or underlying beds, but has been generated by the transforma- 

 tion of organic matters in the strata in which it is met with. This 

 conclusion is in accordance with that arrived at by Mr, S. P. Wall, in 

 his recent investigations in Trinidad. He has shown that the asphalt 

 of that island and of Venezuela belongs to strata of the tertiary forma- 

 tion, (of upper miocene or lower pliocene age,) which consist of lime- 

 stones, sandstones and shales, associated with beds of lignite. The 

 bitumen is found not only in the famous pitch lake, but in situ, where 

 it is confined to particular strata, which were originally shales con- 

 taining vegetable remains ; these have undergone "a special mineral- 

 ization producing a bituminous matter instead of coal or lignite. This 

 operation is not attributable to heat, nor of the nature of a distilla- 

 tion, but is due to chemical reactions at the ordinary 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 palaj- 

 ozoic strata, which in Canada and the United States furnish such 

 abundant supplies of petroleum. In the great palasozoic 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 oxydation and volatilization the naphtha 

 or petroleum, as we have already explained, becomes slowly changed 

 into asphalt or mineral pitch, which is solid at ordinary temperatures. 

 It would even appear that by a continuance of the same action the 

 bitumen may lose its fusibility and solubility, and become converted 

 into a coal-like matter. Thus in the calciferous sandrock in New 

 York a black substance, which has been called anthracite, occurs in 

 cavities with crystals of bitter spar and quartz. It sometimes 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 sub- 

 sequently hardened as a layer above the crystals, which have con- 

 formed to them, showing that this coal-like matter was once in a plastic 



