354 CALIFORNIA ACADEMY OF SCIENCES. 



period. The first is the presence of land and fresh water 

 deposits beneath the recent marine deposits and above the 

 upturned and eroded Merced series. The other is the 

 evidence gained from a topographic study of San Fran- 

 cisco Bay and neighborhood. Such a study as recently 

 pointed out by Prof. Lawson* shows the strong resem- 

 blance of San Francisco Bay, of Rodeo Lagoon, Tomales 

 Bay, Walker's Creek, Drake's Bay, Bolinas Bay, the 

 valley of Lake Merced, etc., to sunken and submerged 

 valleys. 



The question of the order of the above events is an 

 open one. Prof. Lawson makes the land period followed 

 by a slight submergence the last events. The fact that 

 the marine deposits overlie land deposits has led the writer 

 to place the recent submergence as subsequent to the land 

 period, and in its turn it to precede the still more recent 

 uplift to present conditions. 



It is possible that a double movement would explain all 

 the evidence. Aside from the water-worn boulders capping 

 the foothills south of San Francisquito Creek, the marine 

 deposits noticed are confined to the lower levels, about one 

 hundred feet on the bay side, up to over two hundred feet 

 on the ocean side, and higher still in the bench fillings of the 

 streams running into the bay. This theory would give 

 the following record of events: First, submergence to a 

 depth of from 1600 to 1800 feet. , Second, uplift of about 

 1200 feet. Third, uplift to nearly 400 feet above the 

 present level, according to Prof. Lawson, f followed by 

 long period of subaerial erosion. Fourth, submergence 

 to topographic shore-line of present valley. Fifth, slow 

 uplift to present height. (See fig. i.) 



This theory would account for some of the flooded 



* Univ. of Gal., Bull. Dept. GeoL, vol. i, p. 263. 

 t Univ. of Cal., Bull. Dept. of GeoL, vol. i, p. 267. 



