OCEAN DEEPS 21 



to south-west that is, in a similar direction to the mountain 

 ridges in the south-west of Ireland, Cornwall, and Brittany. 

 The southern part of the North Sea is only recently derived 

 from the land, certainly since the Ice Age. 



Here the trawlers not infrequently take in their trawl-nets 

 bones of the mammoth, rhinoceros, bison, and wild horse 

 from the Dogger Bank, proving that the Bank was until 

 recent times dry land. Jukes Brown believes that the Silver 

 Pit (to the south of the Dogger) is the ancient bed of the Rhine, 

 to which the rivers of the east of England were at one time 

 tributary. 



OCEAN DEEPS. 



Areas of the ocean where the depths are over 3,000 fathoms 

 are called "deeps" (German, Graben). These deeps are 

 variously named. Sir John Murray named them, according 

 to no definite plan, with the name of some hydrographer or 

 exploring vessel. Foreign oceanographers usually name 

 according to their geographical position e.g., Tonga Deep. 

 The ocean deeps aggregate 9 million square miles that is, 

 6*65 per cent, of the ocean floor. The number of recorded 

 deeps is 57, of which 32 occur in the Pacific, 5 in the Indian, 

 and 19 in the Atlantic Ocean. One is partly in the Indian 

 and partly in the Atlantic Ocean. 



One additional feature of the oceanic deeps must be 

 mentioned. They are often trough or trench shaped and 

 close to continental land, though some are of irregular outline 

 or basin-shaped. Practically every deep has its corresponding 

 mountain fold, and, in fact, all the deeps lie near and parallel 

 to recent folds in the earth's crust. In some cases the vertical 

 distance from the greatest depth of a deep to the peak of the 

 highest mountain in the associated mountain fold is remark- 

 able. In the deep off Japan soundings of 4,655 fathoms, or 

 27,930 feet, have been recorded ; if this be added to the height 

 of Fusiyama, 12,400 feet, we get a vertical distance of 40,330 

 feet. Similarly off the west coast of Northern Chili there are 



