BITUMEN, PETROLEUM, AND NATURAL GAS. 



387 



although combustible gases may issue from decomposing organic matter 

 of any kind, or from coal. Some of the burning springs in the oil- 

 region of Kentucky are said to produce a flame twenty to thirty feet 

 long. It is a significant fact that petroleum is often associated with 

 salt. It is so in Pennsylvania, in Virginia, and in many other localities. 



Oil-Formations. — I have said that petroleum and bitumen are found 

 in all fossiliferous formations, but in each country there are certain for- 

 mations where it especially abounds : in Europe it is found principally 

 in the Tertiary ; in Eastern United States it is found almost wholly in 

 the Palaeozoic, below the Coal-measures ; in California it is found in the 

 Tertiary. 



Principal Oil-Horizons of the United States. — In Pennsylvania and 

 Kentucky oil is found in the Upper Devonian ; in Canada and Michigan, 

 in the Lower Devonian ; in Western Virginia it is found in the sub- 

 Carboniferous ; in Ohio, in Lower Coal-measures, in the Upper De- 

 vonian (Huron shales), and even in the Lower Silurian (Trenton lime- 

 stone) ; in California it is found in the Miocene Tertiary of the Coast 

 Kange, all the way from Los Angeles to Cape Mendocino. These have 

 been called oil-horizons. 



Laws of Interior Distribution. — The mode of interior distribution 

 of petroleum and bitumen is similar to, yet different from, that of 

 Avater. Like water, it occurs in porous strata and collected in fissures 

 and cavities ; like water and with water, it issues in hill-side springs ; 

 like water and with water, it collects in ordinary wells, or sometimes 

 spouts in immense quantities from artesian wells. Some of the great 

 spouting- wells of Pennsylvania, when first opened, yielded 3,000 barrels, 

 some in Ohio 5,000 barrels, 



and some of the great wells & c Jb^ «^ 5 



of Baku, on the borders of the 

 Caspian Sea, even 1,000,000 

 gallons per day. But, unlike 

 water, there is no perennial 

 large supply ; the accumula- 

 tions of ages being exhausted 

 in a few months or a few 

 years. Unlike water, the force 

 of ejection in great sp outing- 

 wells is ae£ hydrostatic press- 

 ure directly, but the pressure of elastic gases generated from the petro- 

 leum ; though, as Orton has shown, the elastic compression of these is 

 probably due to hydrostatic pressure. The great spouting -wells, being, 

 therefore, the fortunate tappings of reservoirs which have been accumu- 

 lating for millenniums in great fissures and cavities, are enormously 

 productive, but also rapidly exhausted. It is evident that the same is 



Fig. 517. 



