40 



CRANDALL— SAN FRANXISCO PENINSULA. 



[January 4, 



As a result of this breaking up the diabase outcrops are irregularly 

 scattered through the serpentine areas. The sills at the Presidio 

 and Potrero show the presence of two different serpentine intru- 



Fig. 18. 







A place in the cliffs north of the Presidio where the serpentine is intruded 

 into the shales of the Telegraph Hill beds. 



sions; whether they both occurred at the same time or at different 

 times is not clear. 



Sections through these different sills show their structural fea- 

 tures plainly. 



V. Physiography. 



The main features of the topography of the northern end of 

 the peninsula are controlled by the major faults, giving as a result 

 two large blocks tilted toward the northeast, and one block with 

 complex folding. The northwest-southeast trend of Buri-Buri 

 ridge, San Bruno Alountain and the line of jasper hills across the 

 city from the Cliff House to Hunter's Point is characteristic of the 

 Coast Range ridges that are determined by major and minor faults 

 and major folds. These features are plainly shown in the accom- 

 panying photograph of a relief map of the peninsula made by A. H. 

 Purdue, of Stanford University. 



