CH. Il] THE OCEANOGRAPHY OF THE NORTH-WESTERN OCEAN 83 



(10 fathoms) is reached only after we get 10 miles or more fi-om 

 the land. Even if we make a traverse of the North Sea between 

 the Wash and the Texel on the coast of Holland, a distance of 150 

 nautical miles, we do not find water which is more than 10 fathoms 

 in depth. In such parts of the sea the sandy foreshore is continued 

 out as a flat sandy sea bottom underneath shallow water. In 

 other places the coast-line descends more or less precipitously into 

 the sea and we find a rocky shore covered with sea-weed. Passing 

 out to sea from such a shore we soon encounter the " Laminarian 

 zone," the portion of sea bottom covered with the giant fronds of 

 the sea- weed Laminaria, and affording shelter for a varied 

 assemblage of marine animals. 



Sea bottom deposits. Outside the narrow region of coastal 

 waters, the extent of which depends on the steepness of the 

 continental slope, we come upon a sea bottom which is much less 

 prolific in life than that which we have been considering, and the 

 nature of which is very different. From the coast-line out to the 

 edge of the continental shelf, at a depth of 200 metres,, we have 

 the region of the " terrigenous " sea bottom deposits. Near the 

 land where the sea deepens rapidly, and over wide areas such as 

 the North Sea in its southern portion, and the whole of the Irish 

 Sea with the exception of the deep " gutter " between the coast of 

 Ireland and the Isle of Man, the sea bottom consists of boulders, 

 gravel and sand, all materials which result from the detrition of 

 the land and the erosion of the coast-line. Sand and mud are 

 carried in suspension by the water or are rolled along the sea floor 

 by the action of tides and currents and arc laid down evenly, 

 forming flat areas of sea bottom with shallow inequalities or 

 channels. Finer particles of mud are carried further and are 

 deposited at a greater distance from the land. We find therefore 

 that as we pass out beyond the edge of the continental shelf the 

 bottom deposits become finer and finer until we reach in deep 

 water the area of the terrigenous blue and green muds. But while 

 such materials resulting from the waste of the land are, generally 

 speaking, characteristic of the sea deposits within the 2000-metre 

 line we yet find others which have a different origin. These are 

 the " Benthic " deposits. While the terrigenous sea floor has in 



J. F. 3 



