WORK OF THE OCEAN 



Characteristics of shallow-water deposits. Clastic sediments 



laid down in shallow water have several distinctive characteristics. 



While they are coarse as 

 a whole, they are char- 

 acterized by many varia- 

 tions in coarseness. The 

 surfaces of successive beds 

 are likely to be ripple- 

 and rill -marked (Figs. 

 196 and 197), and cross- 

 bedding (Figs. 198 and 

 190) is common. Clayey 

 sediments deposited be- 

 tween high and low water 

 may be sun-cracked 

 (Figs. 200 and 201), and 

 the tracks of land ani- 

 mals are in some cases 

 preserved on their sur- 

 faces. Shallow-water 

 deposits may contain fos- 

 sils of organisms which 

 live in waters of slight 

 depth. These character- 

 istics differentiate sedi- 

 mentary formations 

 made in shallow water 

 from those made in deep 

 water, even after they 

 have been converted into 



solid rock, and after the rock has emerged from the sea. Many of 



these characteristics are, how- 

 ever, shared by deposits made 



by streams on land. Subaerial 



and lacustrine sediments are 



distinguishable from those 



made in the sea by their fossils, I 



their distribution, etc. a 



Shallow-water deposits 



have, on the whole, a rather Fiy;. 108. Cross-bedding. (Gilbert.) 



Fig. 197. Rill-marks resembling impressions 

 of seaweeds. Beach at Noyes Point, R. I. 

 (Walcott, U. S. Geol. Surv.) 



