Conditions of life in the sea : a short account of quantitative marine biological research / by James Johnstone.

  • Johnstone, James, 1870-1932.
Date:
1908
Catalogue details

Licence: In copyright

Credit: Conditions of life in the sea : a short account of quantitative marine biological research / by James Johnstone. Source: Wellcome Collection.

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    (10 fathoms) is reached only after we get 10 miles or more from 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 cairied in suspension by the water or are rolled along the sea floor by the action of tides and currents and are 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