GEOLOGY OF SAN FRANCISCO PENINSULA 75 



tain has been forced up through the strata in the manner of a tele- 

 scopic thrust appears to me to have an important element of truth 

 in it. This thrust probably resulting from lateral compression pro- 

 duced the elevation of the granite, partly, at least, through shearing. 



It would appear that the evidence in favor of the successive 

 appearance of the "two dominant fault blocks" is exceedingly 

 slight. While the San Bruno Mountains are considered to have 

 been above the sea level and the Pliocene undergoing erosion, 

 there is believed to have been no such subaerial period for Mon- 

 tara Mountain until the final uplift resulting in the terrace 

 deposits. This is opposed to the observation of Mr. Ashley' as 

 well as to my own views concerning the general post-Pliocene 

 elevation of the coast. By this elevation I do not mean that to 

 which the terraces are due, but an earlier one resulting from 

 the same influences which deformed the Pliocene sediments the 

 whole length of the California coast. 



In regard to the age of the granite Professor Lawson ^ says : 

 "The simplest and most natural hypothesis that suggests itself 

 is that the granite corresponds in age with that of the Sierra 

 Nevada, and this hypothesis has not yet been exhausted of its 

 strong probability of truth. The granites of the Sierra Nevada, 

 in so far as their age is known, are clearly post-Jurassic. Gran- 

 ites of about this age are extensively developed along the west 

 coast of North America from Alaskasouthward. The granites of 

 the southern and northern Coast Ranges seem to be geologically 

 continuous with those of the Sierra Nevada. The fact that the 

 Sierra are separated from the Coast Ranges by the valley of Cal- 

 ifornia is immaterial to the discussion, since the latter is clearly 

 a delta-filled geosyncline of late Tertiary or post-Tertiary origin. 

 There is therefore a strong presumption in favor of the view 

 that the granites of the Coast Ranges and those of the Sierra 

 Nevada are of common origin and common history. This pre- 

 sumption must be steadily kept in view till it is negatived by 

 positive evidence." 



'Neocene Stratigraphy of the Santa Cruz Mountains, p. 334. 

 = Am. Geol., June 1895. 



