50 DYNAMICAL GEOLOGY. 



and burs at the mouths of rivers are, in fact, one form of 

 submarine bank. 



The best examples of banks formed by tidal current* 

 are found in the North Sea. It is seen in the map. Fig. 

 25, that the tidal wave from the Atlantic, striking on the 

 British Isles, divides into two parts, one entering the North 

 Sea through Dover Strait, the other by the Shetland and 

 Faroe Islands. That through Dover Strait runs swiftly 

 through the narrowing channel, gathering much sediment. 

 As soon as it passes Dover Strait it spreads fanlike, its 

 velocity is checked, and it deposits sediment. In the 

 mean time the other branch, coming in from the north, 

 meets the southern branch, and makes still water at some 

 point, as a, and deposits sediment. Again, all the rivers 

 emptying into this sea from the south form bars at their 

 mouths. To these several causes are due the numerous 

 banks which render the navigation of this shallow sea so 

 dangerous. Banks are formed also by oceanic currents. 

 For example, the Gulf Stream, passing through the Straits 

 of Florida, eddies on both sides and forms the Bahama 

 and Florida Banks. Again, the Banks of Newfoundland 

 are at least partly formed by the Arctic current bearing 

 icebergs loaded with debris from Greenland (see pp. 66, 

 67), meeting the warm Gulf Stream, whereby the bergs 

 are melted and their burden dropped. 



Land formed by the Agency of Waves. We have 

 spoken of waves only as destroying land, but under suita- 

 ble conditions they also form land. On submarine banks, 

 however produced, islands are formed by waves. When 

 by sedimentary deposit the bank is built up to near the 

 water-surface, so that the waves touch bottom and form 

 breakers, then the bank is beaten up above the surface 

 and forms islands, which continue to grow by the same 

 agency. Such islands are always low, narrow, and long 

 in the direction of the coast-line. In this way are formed 

 the small islands which overdot the surface of extensive 



