280 University of California Publications in Geology [Vol.11 



The earths and shales contain considerable amounts of hydro- 

 carbons and the term "bituminous shale" or "bituminous slate" is 

 often applied to them. The bituminous shales vary in color from 

 pale gray, through cream color, and various shades of chocolate 

 brown and purplish to dead black. The color is due largely to the 

 presence of variable amounts of bituminous matter. This can be seen 

 in thin sections as irregular streaks of yellowish to brown material. 

 Its presence may also be shown, even in the whitest varieties, by heat- 

 ing a fragment of the shale on a piece of platinum foil until redness 

 is reached. The shale, on heating, first turns black; this color gradu- 

 ally burns away and the shale assumes a white or a pale gray color. 

 If much iron is present it becomes yellowish or yellow brown. During 

 the heating a characteristic odor is developed. 



The black shales are often found to contain enough bituminous 

 matter to burn alone when once ignited. In southern California such 

 shales have, in places, become ignited by brush fires and burned for 

 some time. 22 On fresh fractures, some of these show distinct streaks 

 of oil. On breaking the black bituminous shales with a hammer a 

 strong odor like that of kerosene may be noticed. Black shales of this 

 type can be recognized at a distance in cliff sections from the fact 

 that they weather with a pale blue color, produced by the presence of 

 a thin white coating over the black shale. Some black shales contain 

 numerous foraminiferal shells, appearing as white dots, usually scat- 

 tered irregularly through the black matrix. At times they occur in 

 definite bands, being absent from the shale in intervening spaces. 



The bituminous shales often show a rather regular alternation 

 with other shales or with sandstones. Black shales may alternate 

 with brown shales or with ordinary terrigenous shales ; pale gray 

 shales may alternate with ordinary terrigenous shales, and so on. In 

 such alternations the shale beds are sometimes only a few inches thick, 

 but more commonly they are a foot or two thick and sometimes may 

 be four or five or even ten feet thick. The typical, black, bituminous 

 shale is usually a little harder than the ordinary, lighter colored, bitu- 

 minous or diatomaceous shale. 



In thin section these black, bituminous shales show a fine grained 

 matrix deeply stained with brownish organic material. In sections 

 of ordinary thickness this color is so deep that it is almost impossible 

 to tell the nature of the matrix, without the use of some solvent. 



Embedded in the matrix, there are numerous mineral grains and 

 foraminiferal shells. The mineral grains may make up as much as 



22 Arnold and Anderson, op. cit. 



