Dill 



boulders up to 2 feet in diameter were also observed. Exposed bed- 

 rock has been observed down to depths of 1170 feet and up to the 

 break in slope at 325 feet (Fig. 3). The terraces are less than 100- 

 feet across and the relief of the adjacent cliff is less than 6 feet. 

 The best-developed cliff is between 600 and 700 feet (water depth) and 

 is known from, dredging and echo-sounding traverses to extend con- 

 tinuously for at least 10 miles along the continental slope off San 

 Diego, California. Although large when viewed from the window of a 

 submersible, the narrow terraces and rock cliffs are only barely dis- 

 cernible on echo-sounder traces because of the lack of definition 

 within the wide angle of most sound cones and the relatively high 

 speed at which most surveys are run across the continental slope. 

 In many instances it would be difficult to differentiate between irreg- 

 ularities on the echo-sounder trace caused by high-sea surface swell 

 and those caused by bottom irregularities. 



The terraces and cliffs are narrow zones of acoustically differ- 

 ent bottom that extend for great distances along the continental ter- 

 race. The bottom between the rocky zones are blanketed with a thick 

 (over 10 feet) deposit of fine-grained, silty clays of uniform compo- 

 sition. 



Associated Shallow Water Fossils 



Dredge samples at the terrace level have been analyzed by Dr. 

 Edwin Allison of San Diego State College who states they contain a 

 mixture of fossil and modern species. Associations of the fossil 

 species from a "beachrock" sample taken at a depth of 600 feet dur- 

 ing Dive 175 (see Fig. 2) indicate water depths no deeper than 60 

 feet existed when they were living and that the water was colder than 

 exists at 60 feet in the present latitude of San Diego County. The fol- 

 lowing species are indicative of the above environment: 



Olivella baetica Marrat in Sowerby, 1871 



Turritella cooperi Carpenter, 1864 



Acila (truncacila) castrensis (Hinds, 1843). 



Associated mollusks and micro-fossils from other samples 

 taken along the continental slope off San Diego support the shallow - 

 water origin of the fossils associated with the sea cliffs and found 

 on the terraces. Abundant Foraminifera in the sediment collected 

 during the DEEPSTAR dives include the following species indicative 

 of similar shallow depths: 



Casidulina tortuosa Cushman and Hughs, 1925 

 Cassiduling limbata Cushman and Hughs, 1925 

 Elphidium crispum (Linnaeus, 1758). 



110 



