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University of California. 



[Vol. 2. 



moderately coarse-grained and soft, yielding readily to the action of 

 the weather, and are often excavated by the wind into small caves 

 and hollows. 



On Tomales Point a light yellow sandstone overlies the granite 

 along its eastern border, and in places extends to the water's edge, 

 along the shore of the bay. At the beach, west of Skinner's Ranch, 

 an excellent section of the rocks is exposed in the cliffs. Resting 

 upon the granite is a series of sedimentary rocks consisting of (1) a 

 few feet of coarse conglomerate; (2) a yellowish sandstone, more or 

 less massive, about one hundred feet in thickness; (3) sixty feet or 

 more of whitish, thin-bedded shale. The series is entirely conform- 

 able, and doubtless all belongs to the same period of sedimentation. 



The sandstones of the peninsula have apparently been derived 

 largely from the granite and consist of coarse quartz sand, scales 

 of mica, and kaolin-like material, all of which diminish gradually as 

 one ascends the series. The dip of the series varies with its loca- 

 tion. On Tomales Point it is about 20 toward the southeast, and 

 away from the cliffs facing the ocean. There can be little doubt 

 that here as well as at the lighthouse ridge a large body of granite 

 has been worn away by the action of the waves. The granitic rocks, 

 lying off shore at both places, give evidence of the same thing. 



Figure i.— Section drawn northeast and southwest through Whittenberg Hill. 



Along the summit of the ridge, west of Point Reyes Station, 

 there are sandstones, similar in character to those already described, 

 overlying the granites and metamorphic limestone. It has here a 

 thickness of about one hundred and fifty feet, which has been well 

 exposed by faulting. The sandstones dip steeply to the west and 

 are overlain in places by remnants of thin-bedded shale, and they 

 probably also extend beneath the white shale that makes up the 

 body of the lower hills lying toward the west. Along the western 

 slopes of Vision Hill and in Bear Valley a similar sandstone occurs 

 in the same relation to the granite and white shale. Along the 

 western shore of Drake's Bay are sandstones of a loose, crumbling 



