THE HAUNTS OF LIFE 83 



Physical Conditions 



(1) Depth. — ^The average depth of the sea is about 2| 

 miles, and over 80 per cent, of the sea-floor lies at a depth 

 of over a thousand fathoms. Thus the greater part of the 

 Deep Sea is very deep. It is, indeed, a remarkable fact 

 that the great abyssal plain, deeper than 1,700 fathoms, 

 extends over about 100 milhons of square miles, which is 

 more than a half of the entire superficial area of the earth 

 (197 million square miles, of which 57 millions, say 30 per 

 cent., are terrestrial, and 140 millions, say 70 per cent., 

 are marine). 



Here and there in the Deep Sea there are tremendous 

 depths, technically called ' deeps', of over 3,000 fathoms ; 

 and eight soundings of over 5,000 fathoms have now been 

 taken. Among these is the famous ' Challenger deep * 

 in the North- West Pacific, of 5,269 fathoms, nearly six 

 miles, in which Moimt Everest would be more than en- 

 guKed. In fact, its summit would be 2,600 feet below the 

 surface. Another instance is the ' Swire deep ', off Min- 

 danoa, of 5,348 fathoms, over six miles, in which Mount 

 Everest might be submerged with 3,087 feet to spare. It 

 is easy to calculate the vertical distance between the top 

 of Moimt Everest and the foot of the Swire deep. 



(2) Pressure. — From the weight of water, which great 

 depth implies, it follows that there must be enormous 

 pressure in the Deep Sea. At 2,500 fathoms it is 2^ tons on 

 the square inch, perhaps twenty- five times as much as the 

 pressure in the cylinder of an engine that drives an average 

 railway engine. Even the water is compressed and bodies 

 into which the water cannot penetrate quickly enough are 

 squeezed almost beyond recognition when they are sunk 



