290 CALIFORNIA ACADEMY OF SCIENCES. 



this period there was no folding but simple uplift with the 

 axis of uplift as before in the axis of the range. The 

 shore lines show that these movements of subsidence and 

 uplift rested at a number of levels, the lowest subsidence 

 being at least 1500 feet* below the present level. Prof. 

 Lawson proposes as an hypothesis to differentiate the 

 Pliocene and Quaternary; " that the Pliocene corresponds 

 to the period of more or less continuous depression of 

 the coast; and that the Quaternary corresponds to the 

 more or less continuous uplift which has affected the coast 

 since the maximum depression was reached."! This 

 hypothesis would seem to meet the conditions along the 

 southern coast, but will not those north of Monterey Bay, 

 where the Pliocene has been upturned and eroded before 

 the Quaternary was laid down and where land deposits 

 form the bottom of the Quaternary. In that region the 

 difference in the character of the uplift must be used, 

 the Quaternary being only gently upraised and nowhere 

 dipping more than a few degrees, while the Pliocene is 

 lifted to angles of from 20° to 80°. 



The movements of the Quaternary may be summarized 

 as follows : 



I St. The post-Merced uplift folded the strata of the 

 Santa Cruz Mountains. Subsequent erosion reduced 

 them to base level. Movements aggregating 1000 to 1200 

 feet raise this plane, and again erosion produces marked 

 benches. 



2d. Uplift to a level nearly 400 feet above present 

 level. Land period. Abundant ^olian and sub-aerial 

 deposits. San Francisco Bay a valley. 



3d. Submergence bringing shore line of San Francisco 

 Bay to the foothills, producing benches on coast. Pres- 



*Univ. of Cal., Bull. Dept. of Geol., vol. i, p. 157. 

 t Univ. of Cal., Bull. Dept. of Geol., vol. i, p. 57. 



