236 RESEARCHES UPON THE CHEMICAL PROPERTIES OF GASES. 



cially when it is considered that no other process in nature has been found to yield 

 a gas at all similar in composition to that found in the rocks. 



Of the three hypotheses which have been proposed to account for the production 

 of oil and gas, two are open to a serious objection. 



The chemical changes supposed by Engler to have been the cause, would prob- 

 ably yield gas difterent in composition from the natural gas now being obtained in 

 such large quantity in Western Pennsylvania, and if the gas originally contained 

 ethylene and carbon monoxide it is not easy to explain their complete disappearance 

 in the natural gas I have examined from wells scattered over so large a region. 



The hypothesis of Mendeleeff would be much more difficult to reconcile with 

 the facts as regards composition. The total absence of hydrogen could not be easily 

 explained. The only process in nature which is known to yield gas similar in its 

 constituents to natural gas is that which occurs in swamps and decaying masses of 

 submerged vegetable i-emains. 



The important fact that the solid plant tissues may be preserved for long 

 periods after the preliminary gas evolution has ceased shows that the remains are 

 likely to become slowly buried, to undergo the " fermentation " changes leading to 

 the production of methane. 



Animal tissues can suffer no such arrest of decomposition. Decay once set in 

 is carried rapidly onward to complete destruction without intermission. The con- 

 trast between the conditions in which animal and plant remains occur in the rocks 

 seems to justify this statement. 



If chemical evidence shall count in the discussion, it is difficult to find a more 

 satisfactory explanation than the older hypotheses which the geologists advanced, 

 although in their treatment of the subject the strictly chemical arguments were 

 neglected. 



