870 . , GEOLOGY. 



cri 



though the former decrease as depths which exclude the sunhght are 

 approached. 



Both httoral deposits and deposits in shallow water outside the 

 littoral zone have already been referred to in connection with the work 

 of waves and currents (pp. 355-66). A few additional points only need 

 here be added. 



In general the coarser sediments are lodged near shore and those 



y/Tmn.^ 



Figs. 321 and 322. — Diagrams showing how shallow-water deposits may attain con- 

 siderable depth by the shifting of the zone of deposition seaward. 



farther from the land become progressively finer. Even the coarser 

 part of the material carried in suspension by the undertow is partly 

 left in the shallow water. On the other hand, waves of exceptional 

 strength may carry coarse material into water of some depth. Thus 

 coarse shingle (gravel) and even bowlders have been found at depths of 

 10 fathoms.* Coarse deposits may extend far out from land if the 



^ Fig. 323. — Diagram showing the interwedging of gravel-, sand-, and mud-beds. 



waves are strong, and especially if the water is shallow, and since the 

 zone of shallow water may be extended seaward by the aggradation 

 of the bottom, shallow-water deposits may cover extensive areas. 

 They may become deep at the same time, for as the outer border 

 of the shallow-water zone is shifted seaward by aggradation, the ver- 

 tical space to be filled becomes greater (compare Figs. 321 and 322). 



» Stevenson. Harbors, 2d ed., p. 15. 



