Anderson.] 



Point Reyes Peninsula. 



153 



explained as a reactionary result of humous acids that are known 

 to originate in the decomposition of organic tissues. The effects 

 of these acids upon organic silica have been the subject of a study 

 by Julien to which reference is made. The volcanic origin of 

 much of the total volume of rocks in this series (Monterey) is also 

 fully recognized for other portions of the coast. 



The Miocene sediments lie in a broad syncline resting at both 

 margins upon the granite. Its folding has been affected by move- 

 ments of the orographic block during post-Miocene times which 

 at the same time resulted in a great amount of faulting and the 

 vertical displacement of one of the contiguous blocks to the extent 

 of at least 2,000 feet and perhaps more. 



Pleistocene deposits are strewn over the peninsula and rest 

 generally in an undisturbed position upon all parts, making it appar- 

 ent that the last great movements of the region have affected 

 equally both orographic blocks here referred to, showing plainly 

 that the faulting antedates entirely the Pleistocene Terrace Forma- 

 tions and that it was probably progressive in its development 

 from the opening of the San Pablo epoch, beginning with the 

 subsidence of that time 



Geological Laboratory \ 



University of California, May, i8gg. 



