THE OCEAN AND ITS WORK 



235 



of the embankments is brought in from slightly different directions 

 at different times. The variation in the direction of the waves of 

 succeeding storms often produces a cross-bedding very characteristic 

 of littoral deposits. When the direction of an air or water current 

 changes, the tops of the cross-bedded layers are often eroded away. 

 Later other cross-bedded layers may be laid down on this erosion 



Fig. 228. — Cross-bedded sandstone. (U. S. Geol. Surv.) 



surface. The upper and lower surfaces of a bed of sand may be 

 parallel with each other, as well as with the bottom upon which they 

 rest, yet the laminae of which it is composed may be inclined at an 

 angle of 30 , or more (Fig. 228). 



Littoral Deposits 



Extent. — Littoral deposits are those which accumulate on that 

 portion of the shore which is exposed between high and low tide, and 

 during exceptional storms or tides above high-water mark. They 

 are most extensive in estuaries where the salt marshes are flooded 

 at low tide, the breadth depending upon the slope of the bottom and 

 the height of the tide. The average width of the beaches of the 

 world does not exceed one half mile, and it is estimated that the littoral 



