THE NONMKTALLIC MINKUALS. 433 



inward on both tsides and coniini;' to the siu'facc almost vertically on 

 the rit»"ht. and more nearly horizontally on th(> left (the south). The 

 tunnels are driv^en into the nearly vertical face of the mountain and 

 the oil-hearinj^- rock is protected l)v some TOO or 800 feet of overlying 

 shales. The oil obtained is the lightest thus far found in southern 

 California. On the other hand, the material which exudes on the 

 north side, when the shales are upturned at such an angle as to give 

 free access to atmospheric agencies, is in the form of maltha, or min- 

 eral tar. and so viscous, in December, ISOS, that it could be gathered 

 and rolled into balls like dough. 



The relationship between petroleum and natural gas is scarcely bettei' 

 detincd. That the gas can be derived from petroleum is undoubted, 

 and indeed the latter apparently never occurs free from gas. But on 

 the other hand, as Professor Orton states, the gas often originates 

 luider many conditions in which petroleum does not occur. The 

 formation of marsh gas from decomposing j)lant remains on the bottom 

 of stagnant pools, and its presence in coal mines would show with 

 seeming conclusiveness that a part, at least, of the gas is formed quite 

 independentlv of petroleum. It would seem on the whole most 

 probable that no one theory was universally applicable to all cases. 



Marsh Gas; Natural Gas. — This is a colorless and odorless gas 

 arising from the decomposition of organic matter protected from the 

 oxidizing influence of atmospheric air. By itself it burns quietly, with 

 a slightly luminous flame, but when mixed with air it forms a dangerous 

 explosive. It is this gas which forms the dreaded Are damp of the 

 miners. In small quantities this gas may be found and collected, if 

 desired, from the bottom of shallow pools and stagnant bodies of water 

 by merely disturbing the decomposing plant matter at the bottom, 

 when the l)ubbles of the gas will rise to the top. Under this head may 

 properly be consid(M-ed the so-called iHifiiral (/<ix, which has of late years 

 become of so much importance from an economic standpoint. This gas 

 is, however, by no uK^ans a simple compound, but a variable admixture 

 of several gases, samples from different wells showing considerable 

 variation in composition, as well as those from the same well collected 

 at different periods. This last is shown by the seven analyses following, 

 and which may serve well to illustrate the average composition, though 

 in some instances the percentage of marsh gas has been found greater.^ 



' From Orton's Report on Petroleum, Natural Gas, and Asphalt in Kentucky, pp. 



108-110. 



NAT MUS yy 28 



