Anderson.] 



Point Reyes Peninsula. 



143 



at Point Reyes. The terrace is best developed on the southeastern 

 margin, or perhaps it may be here only better preserved. 



STRUCTURE. 



Crust Block.- — The peninsula of Point Reyes, including the 

 hilly coastal border south of Bear Valley reaching to Paulinas Bay, 

 constitutes an orographic block that has in its oscillations during 

 later geological periods been largely independent of the adjacent 

 mainland. The eastern boundary of this block is the Baulinas- 

 Tomales depression, which reaches the ocean in the two opposite 

 directions. The submarine limits are not so apparent, though there 

 is no reason for believing that they lie within that of the great sub- 

 oceanic declivity situated but a few miles westward. How far the 

 block may extend to the north and south may be inferred from 

 facts only briefly considered here, yet such that leave the question 

 not altogether conjectural. The surface of the block is a shallow 

 basin or trough in which rest the Miocene and later sediments 

 occupying the central portion of the peninsula. Evidently the 

 Farallones form one of the outposts of this orographic block and 

 have participated in all of its principal disturbances, which have 

 probably been in accord with those of the Montara block lying 

 south of the Golden Gate. 



Faults. — The evidences of faulting along the Baulinas-Tomales 

 Valley are to be seen both in the topography and in the general 

 stratigraphic and petrographic relations. East of the valley the 

 long gentle slopes and low rolling ridges of the Franciscan series 

 indicate an old topography, yet the transition to the narrow valley- 

 bottom is abrupt. The western border of the valley is formed by 

 the high, steep ridge of granitic rocks. This ridge is in most 

 places capped by Miocene strata dipping to the westward away 

 from the valley. So far as observed, these Miocene sediments are 

 not to be found eastward of the valley. ■ Either they have never 

 been deposited there, or, as is more probable, they have been so 

 long above water and subject to aerial erosion that they have been 

 all removed. South of Bear Valley, where the rocks of the 

 Franciscan series are more common, there may be still other 



