10 



University of California. 



[Vol. 



acter. The strata are highly bituminous, more especially the lime- 

 stone. The latter appears to be formed almost exclusively of 

 minute organisms. 



The bituminous shales form all of the higher part of the ridge 

 lying east of the spheroidal basalt. The structure of the main ridge 

 facing the south is that of a flat syncline. Toward the north the 

 strata are nearly flat for some distance, so that the banded flints 

 forming the summit on the south are repeated on the tops of the 

 several nearly parallel interlocking ridges. Passing up the main 

 gulch, which heads on the south side of the highest part of the 

 ridge, the gypsiferous clays are seen to be replaced by a yellow 

 earthy variety of the shales. Farther up the hills the strata become 

 harder and lighter colored until they terminate in the flints at the 

 top. Specimens of Pecten peckJiami, Gabb, were found toward the 

 upper part of the series. The hills lying between the head of Cor- 

 ralitos Creek and the Santa Maria Valley diverge somewhat from 

 the main ridge. They belong to the bituminous shale series, but 

 are more earthy than that on the south. They dip away from the 

 Knoxville and the basaltic ridge, and on the northern slope of the 

 hills present a bold front to the valley. On that side they dip into 

 the ridge, that is to the south, thus forming a syncline. 



Petrography. — These rocks present very diverse characters. 

 They vary from those which are almost pure limestone through cal-* 

 careous sandstones and clayey marly rocks to the yellowish white 

 porcelain-like rocks and clear opaline flints. The latter form the 

 upper portion of the great thickness of Miocene strata. They have 

 the same character as in other portions of the Coast Ranges. They 

 are generally well banded, the bands sinking to microscopic propor- 

 tions and often exhibiting a wavy character which may be primary. 

 They vary in color from the light clear opaline variety, through 

 brown with a resinous luster to those which are jet black. They 

 have been affected to a limited 'extent by a secondary action result- 

 ing in the deposition of chalcedonic silica in the cracks and cavities. 

 When examined with the hand lens much of this rock is seen to be 

 thickly specked with little round dots, averaging, perhaps, a milli- 

 meter in diameter. A specimen of the black flints thus marked was 

 chosen for a slide but was found exceedingly difficult to cut. Under 



