4 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [I^OV. 6, 



of fire-clay, coiitainiug fragments of Stiymaria and other coal-plants. 

 In the deeper sinkings, sandstones and bituminous shales are brought 

 up hj the borers ; but in every instance the petroleum appears to 

 be underlaid with a tight stratum of fire-clay. As soon as the oil- 

 bearing stratum is reached, there is usually an escape of carburetted 

 hydrogen gas, and it is discharged with such force that the boring- 

 rods are often blown into the air, as if they had been discharged from 

 a piece of ordnance. The gas is followed by a mixture of oil and 

 gas, and finally by the oil itself, which is thrown in a jet upwards, 

 sometimes to the height of 100 feet. The bore of the well is usually 

 about 4 inches in diameter, being an iron tube let down as the boring 

 proceeds. When the oil appears, the workmen, as soon as they can 

 approach the spot, drive a wooden plug into the iron pipe, and thus 

 prevent the flow of oil, until they are prepared to receive it. Finally, 

 when the natural flow ceases, a pump is applied, and the raising of 

 the petroleum proceeds. Some wells at the outset have produced 

 no less than 4000 gallons of oil in twenty-four hours. At some sites 

 the shallow wells have run out or been exhausted; but by sinking them 

 deeper still greater supplies have been obtained, and which at present 

 appear to be inexhaustible. It seems very certain, therefore, that 

 the reservoirs of oil are fissures penetrating certain oil-bearing strata 

 and the intervening deposits. 



The specific gravity of the petroleums varies from -795 to -881. 

 In general they are of a dark-brown colour. A few wells have pro- 

 duced oils quite clear and transparent ; and simple distillation renders 

 them quite pure and suitable for lamj)s. The inflammability of the 

 vapour of the mineral oil has given rise to accidents. In one case an 

 oil, tapped by a bore at 380 feet, rose in a fountain 100 feet high, 

 was soon afterwards ignited, and burned for two months before the 

 workmen could plug the iron tube. 



After some observations on the antiquity of the use of mineral oil 

 in North America and elsewhere, and on the present condition of the 

 oil- and gas-springs and the associated sulphur- and brine -springs 

 in the United States, the author stated that 50,000 gallons of mineral 

 oil are daily raised for home use and for exportation. The oil-region 

 comprises parts of Lower and Upper Canada, Ohio, Pennsylvania, 

 Kentucky, Virginia, Tennessee, Arkansas, Texas, New Mexico, and 

 California. It reaches from the 65th to the 128th degree of longi- 

 tude west of Greenwich ; and there are outlying tracts besides. 



The oil is said to be derived from Silurian, Devonian, and Car- 

 boniferous rocks. In some cases the oil may have originated during 

 the slow and gradual passage of wood into coal, and in its final trans- 

 formation into anthracite and graphite, — the hydrogen and some 

 carbon and oxygen being disengaged, probably forming hydrocarbons 

 including the oils. In other cases, animal matter may have been 

 the source of the hydrocarbons. 



Other native asphalts and petroleums w^ere referred to by the 

 author, who concluded by observing that these products were most 

 probably being continually produced by slow chemical changes in 

 fossiliferous rocks. 



