468 



LAUGHTON 



[chap. 18 



Worzel (1946), described also by Ewing, Woollard, Vine and Worzel (1946), 

 sliowed some of the typical features of the continental shelf off the east coast of 

 U.S.A., and these studies in the Atlantic have been furthered by Northrop 

 (1951), Owen (1958) and Posgay (1958) on the western side, and Barnes (1955), 

 Vevers (1952) and Wliittard (19(52) on the eastern side. In the north-western 

 Pacific, Sasaki et al. (1957) have studied the shelves off Japan and Zenkevitch 

 and Petelin (1956) those near the Kuril Islands. 



The area off Southern California, which has been called the continental 

 borderland, has been studied in great detail by Shepard and Emery (1941, 

 194()). Emery (1952), Emery and Terry (1956) and many other workers, and 

 the results have been collected together and published in The Sea off' Southern 

 California by Emery (1960). This region is not a typical continental shelf, nor 

 is it typically oceanic. It has islands, basins and trenches with maximum depths 

 of a thousand fathoms, and is separated from both the land and the deep ocean 

 by continental slopes ; it is thus intermediate between shelf and ocean basin. 



A summary of the characteristics of the microtopography of the different 

 physiographic regions is given in Table III, \\'hich has been prepared from a 

 study of all available photographic material both from published papers and 

 private collections of underwater photographs. 



Table III 

 Summary of Microtopographic Features of Different Physiographic Regions 



The continental shelves, excluding the littoral zones, are characterized by a 

 lack of exposed rock. On the other hand, there is a large proportion of a coarse 

 detrital material in the form of gravel, shells and sand. Ripple marks and 

 sand waves are common where there is a sandy bottom, as one would expect 

 from the tidal currents which surround the continents. 



