174 STUDIES IN INSECT LIFE, ETC. 



depth of the pockets in the sea approximates to 

 the height of the highest mountains on the land : 

 roughly they correspond. The greatest depth 

 yet recorded is 5,348 fathoms, and the sounding 

 which registered this was taken east of the 

 Philippines by the German steamer " Planet." 

 It is a few feet more than six English miles. 

 Oceanographically, the term " deep " applies to 

 those parts of the ocean in which soundings of 

 3,000 fathoms or deeper have been taken. In 

 the last map that Sir John Murray published 

 there were fifty-seven " deeps," thirty-two of 

 which lay in the Pacific and but few two ex- 

 ceeding 4,000 fathoms in the Atlantic. From 

 the tide mark down to these depths more than 

 half (in fact 58 per cent.) of the ocean lies be- 

 tween 2,000 and 3,000 fathoms, the average 

 Atlantic depth. The Continental Shelf which 

 fringes our islands and continents is really a 

 marine extension of the neighbouring lands. 

 Many portions of it were in fact dry land not 

 so very many hundreds of thousands of years 

 ago. This shelf is under the influence of tides 

 and currents and the deeper waves, but beyond 

 its edge no wave disturbs the conditions of life 

 at the sea bottom. It is silent Id-bas, it is dark ; 



