300 CALIFORNIA ACADEMY OF SCIENCES. 



tail. It is believed that the strata described by him will 

 be found to belong to the Pescadero series. 



Pet7'ogra^hy and Stratigraphy. — This formation may 

 be described under three facies, the first two of which 

 everywhere grade into each other, the last being more 

 distinct. 



The first is typically developed at Point San Pedro and 

 the neighboring bluffs. The exposure consists of dark 

 and black shales and slates, or shaly sandstones which, 

 while showing finer bedding, is distinctly bedded in layers 

 of from one to three inches or upwards. Many layers of 

 coarse grained, sometimes conglomeritic, grey or white 

 hard sandstone or quartzite occur interstratified in that 

 series. This sandstone, while sometimes heavily bedded, 

 is not in continuous layers, but constantly varying in 

 thickness and sometimes disappearing altogether. At the 

 top of the point, where the nearly vertical shales have 

 been deeply weathered, they have become the same in 

 appearance as the soft yellow sandstones which in other 

 regions have been assigned to the Miocene age, as, for 

 example, the sandstone exposed along the top of the 

 ridge west of Woodside and Searsville. The bedding 

 runs from the shale into the sandstone without break, 

 leaving no doubt that the one is only the weathered pro- 

 duct of the other. In places the joints have been filled 

 with a white mineral like barite. In San Francisco this 

 facies is well shown by a deep cut on Second street, 

 several blocks from Market, also at the corner of Jones 

 and Washington streets. 



The second facies, which is quite common, consists of 

 heavy bedded sandstone, generally of a yellow or brown 

 color where weathered, but a grayish blue in the interior 

 of the strata where not weathered. In some places the 

 beds will average a foot or two thick, the stratification 



