Lithology 



One of the factors that control physiog- 

 raphy in areas of marine erosion is hthology. 

 In addition the mineral and fossil contents 

 of the rocks provide information about the 

 past development of the physiography — in 

 other words, the paleogeography. 



Rock Bottom 



When lead-line soundings were used in 

 past times as the only method of learning 

 about sea floor topography, they showed the 

 common presence of rocky bottom because 

 rocks made scratches on the lead weight, 

 and occasionally pebbles were found em- 

 bedded in tallow that had been put into a 

 small hole in the base of the lead. Even 

 after sonic sounding methods were devel- 

 oped, periodic depth checks by lead line 

 added to the store of information about bot- 

 tom materials. Smooth sounding sheets of 

 the U. S. Coast and Geodetic Survey for 

 southern California, nearly all of which were 

 made before 1937, show about 160 notations 

 of rock bottom in areas deeper than 600 feet 

 and several thousand more in shallower 

 areas. Between 1936 and 1940 large samples 

 of the sea floor were obtained by Shepard 

 and Revelle of Scripps Institution of Ocean- 

 ography, using dredges, covers, and snap- 

 pers. These brought the total number of 

 rock or gravel samples available for study to 



131 for the whole region. On the basis of 

 these samples, the earlier chart notations, 

 the presence of kelp, and an interpretation 

 of the topography, Revelle and Shepard 

 (1939) compiled a map showing the general 

 pattern of bottom materials in most of the 

 region. Rock bottom was shown to exist on 

 shelves, walls of submarine canyons, bank 

 tops, and steep slopes. The actual positions 

 of the samples and notations on which their 

 chart was based are shown on another chart 

 by Shepard (1941). 



Since 1941 few additional data on the 

 regional distribution of rock bottom have 

 been secured; instead, most of the effort has 

 been directed toward intense studies of small 

 areas mostly as graduate theses at the Uni- 

 versity of Southern California and Scripps 

 Institution of Oceanography. Among the 

 most important of these are the shelf off" 

 San Nicolas Island (Norris, 1951), the shelf 

 off" San Diego (Emery, Butcher, Gould, and 

 Shepard, 1952), Cortes and Tanner Banks 

 (Holzman, 1952), the shelf of San Pedro 

 Bay (Moore, 1954a), Santa Rosa-Cortes 

 Ridge (Uchupi, 1954), the shelf of Santa 

 Monica Bay (Terry, Keesling, and Uchupi, 

 1956), the shelf off Santa Catalina Island 

 (McGlasson, 1957), the shelf off Santa 

 Barbara Island (Grady, in preparation), the 

 shelf off Anacapa Island (Scholl, 1959), the 

 sides of San Pedro and Santa Monica Basins 

 (Gorsline, 1958), and Lasuen Seamount 



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