OCEANOGRAPHY. 19 



ocean. Thus the sea-bottom in the neighbour- 

 hood of the land is formed partly by terrigenous 

 deposits, varying of course in character with the 

 geological nature of the land itself, and partly 

 by the animal and vegetable deposits of the 

 coast. In some cases the deposits brought by 

 the rivers can be traced in the sea-bottom for 

 a very great distance from the coast. The 

 characteristic mud of the Congo river can be 

 traced 600 miles from its mouth, and it is said 

 that the Arabian Sea and the Bay of Bengal are 

 carpeted for 1000 miles by the mud brought 

 down by the Ganges and the Indus. Leaving 

 out of consideration, however, for the moment 

 the exceptional cases of such large rivers as these, 

 we may say that the influence of the land 

 deposits upon the character of the sea-bottom 

 extends to a distance seawards of about 250 

 miles. If we had a complete and careful survey 

 of all the coast lines, it would be possible for 

 us to draw a line round the great continents 

 marking the limit of the deposits of river and 

 coast mud. This line has been called the mud 

 line by Mr John Murray, and, as he has clearly 

 pointed out, it is characterised by an abundant 

 and extremely interesting Fauna. 



The sea-bottom, then, within the limits of the 

 mud line, is very largely composed of deposits 

 from the land brought down by the rivers. In 

 some volcanic regions of the world this is, to a 

 great extent, augmented by lava and water-logged 

 pumice, and in other districts by the mud and 

 stones dropped by the melting ice-bergs. The 

 influence of animals and plants upon the forma- 



