282 SKETCHES OF CREATION. 



used for the production of " coal oil," or " Breckenridge 

 oil," some years before the discovery of native petroleum. 

 Hence arose the name " coal oil," which, in some sections 

 of the country, is still applied to refined petroleum, al- 

 though it never had any relations to the Coal-measures. 

 Peat and lignite are capable of employment for the same 

 purposes. 



The deep-seated shales of the earth's crust are inclosed 

 in rocky retorts hermetically sealed. The unquenched 

 fires of the molten nucleus of the planet continue to impart 

 their warmth to the ever-cooling crust. The rocky retorts 

 in Nature's vast laboratory are warmed — their organic con- 

 tents undergo a slow distillation — the products escape in 

 the form of gas or oil, and slowly filter through pores and 

 crevices toward the surface, till intercepted by some imper- 

 vious stratum. These products, from the nature of the 

 case, can not descend. They are lighter than water, and 

 must tend to rise through the water in the midst of which 

 they are disengaged. 



The largest portion of oil and gas thus elaborated es- 

 capes to the surface and is lost. In order to prevent this 

 escape, the retort must be furnished with a closed con- 

 denser or receiver. The exhalation ascending from the 

 mother shale must be intercepted by a stratum of a clayey 

 and impervious character. Beneath this the oil and gas 

 will accumulate, displacing the water previously occupy- 

 ing the space. This reservoir may be an open cavity, a 

 fissure, a shattered stratum of rock, or a mere porous sand- 

 stone. Here the oil will be stored. 



But it is obvious that in the course of time a tendency 

 will be manifest toward lateral extension over an indefinite 

 distance, so that the products will be little concentrated 

 in place, if they do not even find a leak in the roof and 

 slyly escape to the surface. In order that these products 



