I'eckham.] 458 [Seplember IS. 



pheric action soon become brown or black, but the increase in 

 density is very gradual. These changes are not all produced 

 upon the surface, as many of the springs yield maltha of varying 

 density, and wells bored to a depth of from fifty to four hundred 

 feet, have yielded bitumen which had undergone a greater or 

 less change. A careful study of the different exposures over a 

 very wide area, when taken in connection with the above men- 

 tioned facts, convinced me that such changes could not possibly 

 be produced by inspissation, even in the warm climate of South- 

 ern California. I soon became equally well satisfied that they 

 were due entirely to the action of atmospheric air, conveyed 

 through the agency of rain water. Wherever the belt of shales 

 from which the oil primaril}^ issues is exposed in a nearly or 

 quite perpendicular blutf, in which the shales are overlaid with 

 impervious strata of sandstone or by several hundred feet of 

 shales, the oil reaches the surface unchanged ; but Avhen the out 

 crop occurs near the base of a gentle slope, or near the summit 

 of the hills, in situations where the oil shales are horizontall}' 

 exposed to the action of meteoric water over areas of consider- 

 able extent, the bitumen exudes of a densitj^ increased in propor- 

 tion to the amount of exposure to which it has been subjected. 

 The subterranean reservoirs of Penusylvanian petroleum are 

 overlaid by slightly disturbed and inclined strata of impervious 

 sandstones, while the oil shales of California contain few large 

 fissures but innumerable small ones, the fluid being held in them 

 by capillary attraction and between the layers of shale, conse- 

 quently exposing a very large surface of oil to contact with 

 water, w'herever the strata are so exposed as to admit of its 

 infiltration. The strata in that region are very much broken 

 and inclined at ver^^ high angles. 



I became convinced at a very early date in my study of this 

 subject that the difference in exposure alone, would perhaps 

 account for the difference in the average density of the Penn- 

 S3dvania and California oils, but the discover}- of the fact that 

 the latter did not contain paraffine, and that it was not found 

 in oils distilled from them, led me to question the identity of 

 these oils in chemical constitution. 



The researches of Prof. Warren upon volatile hj-drocarbons 

 from various sources have shown conclusively, that ultimate 

 analyses of crude petroleums are of little or no assistance in 



