GEOLOGY. 285 



etable remains; these have undergone " a special mineralization pro- 

 ducing a bituminous matter instead of coal or lignite. This operation 

 is not attributable to heat, nor of the nature of a distillation, but is due 

 to chemical reactions at the ordinary temperature, and under the nor- 

 mal conditions of climate." He also describes wood partially con- 

 verted into bitumen, which last, when removed by solution, leaves a 

 portion of woody tissue. 



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 paleozoic basin 

 of ISTorth 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 oxidation 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 be- 

 come converted into a coal-like matter. Thus, in the calciierous 

 sand-rock 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, ac- 

 cording to Mr. Vanuxem, having been introduced into these cavities 

 in a liquid state, and subsequently hardened as a layer above the 

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

 matter was once in a plastic state. 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 accompanying trap rocks, presenting mammillary surfaces, 

 which evidently show that it has once been semi-fluid. 



An evidence of the presence of unaltered petroleum in almost all 

 the Lower Silurian limestones is furnished by the bituminous odor 

 which they generally exhibit when heated, struck, or dissolved in 

 acids. In some cases petroleum is found filling cavities in these lime- 

 stones, as at Riviere a la Rose (Montmorenci), where it flows in 

 drops from a fossil coral of the Birdseye limestone, and at Pakenham, 

 where it fills the cavities of large orthoceratites in the Trenton. The. 

 presence of petroleum in the Lower Silurian rocks of New York is 

 shown in the township of Guilderland, near Albany, where, according 

 to Beck, considerable quantities of petroleum are collected upon the 

 surface of a spring which rises through the Hudson River or Lorraine 

 shales. On the Great Manitoulin Island also, according to Mr. Mur- 

 ray, a petroleum spring issues from the Utica slate, and he has de- 

 scribed another at Albion Mills, near Hamilton, rising through the 

 red shales of the Medina group ; these have probably their origin in 

 the Lower Silurian limestones, which may in some localities prove 

 to be valuable sources of petroleum. 



In the Upper Silurian and Devonian rocks bitumen is much more 

 abundant ; Eaton long since described petroleum as exuding from the 



