NEOCENE STRATIGRAPHY. 353 



recenty st ood for a considerable time at an elevation of 

 1600 to 2100 feet below its present level.* Evidence of 

 this can be seen in the level summit of the main ridge to 

 the north of Black Mountain. 



Standing upon the hills near South San Francisco sta- 

 tion where a comprehensive view can be obtained of the 

 line of hills extending from Seven Mile-Beach to Red- 

 wood City, between Crystal Springs Valley and the bay, 

 their summits can be seen to present a remarkably even 

 horizontal line. Examined on the ground the top of this 

 line of hills has the aspect of a plateau, from which rise 

 a few sharply conical knobs. These have the appearance 

 of remnants left by the eroding waters which planed off 

 the top of the hills leaving the plateau. Further evidence 

 of such a submergence and erosion is found in the fact 

 that a little further south, where these hills are not sepa- 

 rated from the main mountain ridge by the broad and 

 deep valley', their summits are more or less covered with 

 boulders of metamorphic rocks well water worn. 



Altogether the evidence seems quite strong to show 

 that the Santa Cruz Mountains have very recently been 

 submerged to a depth near San Francisco Bay of at least 

 600 feet. In a later uplift the mountains seem to have 

 stood for some time at a level about loo feet below their 

 present elevation. This has resulted in the marked shore 

 line where the rounded foothills meet the nearly level 

 floor of the valley surrounding the bay. This level floor 

 seems to have been the result partly of erosion and partly 

 of deposition. It seems quite possible that this upward 

 movement is still in progress. 



What preceded this recent submergence? The evi- 

 dence, from two standpoints, would indicate a long land 



*Univ. of Cal., Bull. Dept. Geol., vol. i, pp. 115-160. 

 2d Ser., Vol. V. ( 23 ) August 1, 1895. 



