2(55 CALIFORNIA ACADEMY OF SCIENCES. 



at the bottom of the water deposits, and at the top cover- 

 ing a major part of San Francisco county. 



General Striictiti'e. — As stated above, each of these 

 periods of deposition has been followed by upheaval and 

 erosion. These upheavals have been progressively gentler. 

 On the San Francisco peninsula no distinction could be 

 found between a movement which followed the laying 

 down of the Pescadero series and a post-Jurassic move- 

 ment which it is claimed followed the laying down of the 

 radiolarian cherts and associated rocks.* 



Both formations, whether distinct or not, were subjected 

 to a powerful upheaval, being folded, faulted, crushed 

 until a structureless mass has frequently resulted. The 

 lower or so called metamorphic rocks have generally lost 

 all trace of bedding, the phthanites excepted. In some 

 places they show secondary silicification. The upper beds 

 usually show bedding, though in many places this is lost 

 and secondary silicification appears similar to that more 

 common in the lower metamorphic rocks. High and ver- 

 tical dips prevail in both formations. 



Movement seems to have taken place largely by fault- 

 ing, though the structure taken as a whole appears to be 

 that of an anticline. The bedding of the Pescadero 

 series along the top of the main ridge is generally more 

 or less nearly horizontal, on either flank becoming vertical 

 or nearly so. The Merced and Monterey series were 

 evidently laid down upon and around this anticlinal moun- 

 tain of early Miocene age, and in late Pliocene or in 

 Pleistocene time came another movement which elevated 

 the mountains nearly to their present position. As before, 

 faulting predominates and is the controlling factor in most 

 of those details of the topography due to structure. Many 

 of these faults have a downthrow of hundreds of feet or 



* American Geologist, vol. ix, Mar. 1892, p. 133 et seq. 



