THE WORK OF THE OCEAN 



293 



would be attended by more striking consequences. It follows that 

 the changes effected by diastrophism are much more obvious in 

 shallow water than in deep. Emergence or submergence shifts the 

 zone of contact of ocean and land, and so the areas of aggradation 





Fig. 240. Map showing the early stages in the simplification of a shoreline, 

 and showing that at this stage the irregularities are increased. 



and degradation, and changes the region concerned from one ap- 

 propriate for sea life to one appropriate for land life, or vice versa. 



Over the continental shelves the water is shallow and the bottom 

 relatively smooth. If the sea-level is drawn down, or if the con- 

 tinental shelf is elevated evenly, the new shore-line on the smooth 

 surface of the former submerged shelf will be relatively regular, 

 even though the coast was notably irregular before the change. 

 This is illustrated by Fig. 240. Subsidence of a coast-line (or rise 



