Geol.— \'oL. II.] ANDERSON—STRATIGRAPHIC STUDY 163 



the Lower Miocene. These massive sandstones present 

 many curious and striking examples of atmospheric erosion, 

 among which are the natural cisterns often developed on 

 the summits of the most conspicuous pyramids of rock. 



Along the Eocene belt extending westerly from Tar 

 Springs the rocks stand at a high angle dipping to the north 

 at an angle of 75° to 80°. In the Coalinga belt they likewise 

 stand at a high angle dipping toward the east, while farther 

 north the inclination is less and the strike carries them in a 

 broad curve around the outer flanks of San Benito Mountain. 

 The dip naturally varies in its direction with the strike, but 

 in its inclination it is commonly between 25° and 35°. 



While the stratigraphic divisions of the Eocene do not 

 continue regularly throughout, there is at least one member 

 that is fairly well characterized along the whole extent of 

 the series as far as followed. This member is the middle 

 one, and consists of brown bituminous or carbonaceous 

 shale, more or less sandy in the lower portion, and with 

 a maximum thickness of six hundred feet as exposed on 

 the hills a few miles north of Coalinga. Farther to the 

 south and southeast it varies considerably, attaining at the 

 Kreyenhagen wells a thickness of about nine hundred feet, 

 while on the head of the Jacalitos and on the Zapata Chino 

 there are not more than two hundred fifty or three hundred 

 feet of strata. On account of its development at the Krey- 

 enhagen wells this member of the Eocene has been termed 

 the Kreyenhagen Shales. The lithological character of these 

 shales is not constant, as the proportions of the chief elements 

 vary from point to point. Sands, clay, and organic matter, 

 both calcareous and carbonaceous, make up the mass of the 

 beds, which at some points become sandy and at others argil- 

 laceous, while the percentage of lime or carbonaceous matter 

 also varies. 



Nodular masses of calcareous rock and nodules of barites 

 ( Ba SO4 ) are common in many places, and these form a 

 characteristic feature of the shales. 



The calcareous masses occurring in the shales often con- 

 tain foraminifera in great numbers, not unlike certain rocks 



