SECT. 3] 



ESTUARIES, DELTAS, SHELF, SLOPE 



639 



continental borderland off Southern California by Revelle and Shepard (in 

 Trask, 1939), namely, that "there is no progressive decrease in average grain 

 size with either increasing depth or distance from shore": the general distribu- 

 tion is irregular, and it is not at all unusual to find coarse sediments on the 

 outer shelf. 



During the last fifteen years, a great deal of new data has been gathered 

 concerning shelf sediments, especially in European and North iVmerican waters 

 but also in hitherto little-known areas such as the platform off Venezuela and 



89° 20' 89°10' 89°00' 88° 50' 88°40' 



89° 20 



89 10 89 00 88 50 88 44 



Fig. 17. East Mississippi delta sediment environments. (Slightly simplified from Shepard, 

 1956, fig. 5.) 



Legend — 1: interdistributary bays; 2: delta-front platform; 3: pro-delta slope; 

 4: open shelf recent delta; 5: old shelf deposits; 6: reworked Mississippi delta deposits; 

 7: open inlet deposits; 8: open lagoon deposits. 



Western Guiana where accurate investigations were initiated in 1952 under 

 Kuenen's leadership. The results agree entirely with the provisional conclusions 

 drawn from chart examination. An increase in grain size on the outer shelf 

 is now well established for a large number of areas, and this feature is an in- 

 heritance from Pleistocene conditions, as Stetson (in Trask, 1939) and Daly 

 (1934, p. 206) had already suggested for the New England shelf. 



One of the most striking examples is afforded by the eastern margin of the 

 Mississippi delta (Fig. 17). Although the Mississippi River at present carries 

 to the sea a tremendous sedimentary discharge, averaging perhaps two million 



