54 



University of California Publications. 



[Geology 



sion. At least 500 feet of these shales are represented at Point 

 Pi eves Peninsula. 



SAN PABLO. 



Blue Sandstone (Tuff) of Carneros Creek. — The only strata 

 of undoubted San Pablo age occur as the core of the low range 

 of hills between Sonoma and Petaluma. As illustrated in sec- 

 tion CD, blue San Pablo sandstone occurs on Carneros Creek. It 

 consists of the peculiar and very characteristic bluish to grayish, 

 rather soft sandstone, exactly similar to that described* by Tur- 

 ner from Mt. Diablo and Corral Hollow, which is so common in 

 the Coast Ranges to the south. It is really an impure andesitic 

 tuff. It varies from a gray to deep blue in color, and from a 

 coarse, massive rock to thin bedded shales. At the point where 

 section CD crosses it, it dips at 50° to the southwest and is over- 

 lain unconformably by the Mark West andesite. 



Age. — This formation is unique in appearance, and of wide- 

 spread distribution throughout the Coast Ranges south of this 

 territory, it also occurring on the west flank of the Sierras, where 

 it is placed in the lone formation. Even without the aid of fos- 

 sils it can be unhesitatingly referred to the San Pablo, but at 

 Carneros Creek a good bed of shells of this age exists. So far 

 as the writer is aware, this is the most northerly locality in the 

 Coast Kanges at which it has been encountered. 



SAN PABLO (?). 



In addition to the strata above described, there are certain 

 others which are tentatively referred to the San Pablo. They 

 certainly antedate the Pliocene lava flows of the Coast Ranges, 

 which, it will be shown later probably belong to the later Pliocene. 

 They consist of a variety of sandstones, shales and conglomerates, 

 free from pebbles of volcanic rocks. 



I' n - Volcanic Beds near Freestone. — Between Freestone and 

 the mouth of Tomales bay and the town of Tomales these beds are 

 well exposed, being here some 400 feet thick, and made up about 

 as follows : At the base about 50 feet or more of a very coarse 

 hard sandstone, approaching a conglomerate in texture, most of 

 the grains being well water worn, and composed of chert or* 



•Notes on some igneous, metamorphie and sedimentary rocks of the 

 Coast Eanges of California. Jour. Geol., Vol. 6, No. 5, 1898. 



