ON PETROLEUM AND PHOTOGEN. 29 



or steam power. The average depth at which oil is procured, does not 

 far exceed 250 feet, the strata penetrated being chiefly limestone, 

 sandstone, and shale. Some wells yield 200 barrels jjer day, one in 

 Pennsylvania at the depth of 170 feet yields 300 barrels per day. At 

 the present time upwards of 550 wells are in operation yielding about 

 30,000 gallons of crude oil daily. There are two sources in the West 

 for petroleum springs 1. The oil regions of Pennsylvania and N. E. 

 Ohio, which are on the bituminous coul measures and sandstones of the 

 Portage and Chemung groups. 2. The oil regions of W. Virginia and 

 S. Ohio, including a portion of W. Pennsylvania which are on the coal 

 measures. 



The source and formation of Rock oil is difficult of explanation 

 and has given rise to different and various opinions. One hypothesis is 

 that petroleum has its origin in coal beds, that a low heat in the coal 

 seams drives off hydro-carbon vapour, which is condensed in the pores 

 of the rocks and the soil, and is washed by rains into subterrant ous 

 recesses situated at various depths in the rocky strata ; an evident 

 objection to this explanation is that the coal of the district possesses 

 the natural quantity of hydro-carbon and bitumen. 



Another theory is, that the oil was produced at the time of original 

 bituminisation of the vegetable or animal matter. If this was so, 

 wherever there is bituminous coal, Ave should expect to find correspond- 

 ing quantities of oil. This is not so, there is no oil except in fissures 

 in the rocks overlying the bituminous strata, and these fissures can be 

 shown to have been made since the coal strata became bitumenised. 



Petroleum occurs in rocks of all ages from the lower Silurian to 

 the tertiary ; it is, doubtless, of organic origin, and is generally found 

 impregnating limestone, more rarely, sandstones and shales. The 

 presence of it in the lower paloeozoic rocks which contains no traces of 

 land plants is a sufficient proof that petroleum has not in every case 

 been derived from terrestrial vegetation, but may have been formed 

 from marine plants or animals, or both ; of the latter, the Poole and 

 shale which contains abundant remains of fishes and Crustacea, and 

 affords in distillation a large quantity of illuminating oil is an example. 

 This is not surprising when it is recollected that considerable portions 

 of the tissue of the lower animals is destitute of nitrogen and similar 

 in composition to the woody fibre of plants. Sir W. E. Logan describes 

 the Canadian oil as being yielded by a limestone formed chiefly of fossil 

 corals in the pores of which the oil is stored, so that the oil may be the 

 result of the decomposition of the soft jellylike animalcules, in the 

 same manner as the decay of plants has in later times given rise to 

 bituminous coal. However this may be, the production of petroleum 

 there is every reason to believe is due to the decomposition of organic 

 matter, but the exact conditions under which it is capable of being 

 produced are unknown, or wherefore it should from decomposition 

 rather assume the form of this substance than that of lignite or coal. 

 But in the fermentation of sugar (to which we may compare the trans- 



