316 CLEMENTS 



suggests relative movement of as much as a thousand feet. Regardless of 

 the amount of lowering involved, it is the opinion of the present author 

 that Shepard presents convincing evidence for the fluviatile origin of 

 the submarine canyons. 



SEDIMENTS OF THE SEA FLOOR 



Rounded pebbles and cobbles have been dredged from the sea floor 

 at several places. One of these localities vi^as on w^hat appears to be a 

 submarine terrace extending six miles southeast of Santa Catalina Island, 

 at a depth of 900 feet (Clements and Dana, 1944). From the shape and 

 degree of rounding of the fragments it M^as concluded that they repre- 

 sented a beach deposit, formed when Santa Catalina stood 900 feet 

 higher or sea level was 900 feet lower. Although a possible upper Pleis- 

 tocene age was postulated, it could as readily be assigned to any other 

 part of the Pleistocene. 



Material of similar characteristics and probably also of beach origin 

 was dredged from Cortes Bank at a depth of 300 feet (Clements, 1945), 

 and a ridge extending northwesterly from Tanner Bank yielded like 

 sediment from a depth of 2,862 feet (Emery and Shepard, 1945). Thus 

 the sediments, like the terraces and submarine canyons, suggest wide 

 fluctuations of sea level during the relatively recent geologic past. 



FOSSILS 



In attempting to work out the distribution of sea and land in the 

 Pleistocene, fossils of various kinds — mammals, plants, and inverte- 

 brates — have been found very useful. Fossil elephants have been de- 

 scribed from Santa Cruz, Santa Rosa, and San Miguel Islands by Stock 

 (1935). These elephants are closely related to those found on the main- 

 land at such localities as Rancho La Brea (Stock, 1930) and Centinela 

 Park (Clements, 1937), and thus indicate a land connection between 

 the northern group of islands and the mainland during the Pleistocene. 

 However, the elephants are dwarfed, the dwarfing being more pro- 

 nounced in those of Santa Rosa than those of San Miguel, which lies 

 farther offshore (Stock, 1935). The dwarfing is similar to that shown 

 by the fossil elephants of the island of Malta, and is believed to be the 

 result here, as there, of island environment. The indication is that the 

 islands were connected with the mainland during early Pleistocene time, 

 and were again separated later in the Pleistocene with sufficient time for 



