228 DEEP-SEA DREDGING. 



we are as well acquainted with the contour of large tracts 

 of the sea bottom as we are with many parts of the sur- 

 face of the dry land. The ocean bed is now known to be 

 no flat table-land, like the surface of the water which rests 

 upon it; but to be diversified with plains and valleys, 

 peaks and mountain-chains. Thus, in the Atlantic Ocean, 

 there is a submerged mountain-chain, rising 15,000 feet 

 above the surrounding depths; and some of the oceanic 

 islands, as St. Paul's Rocks, Ascension, and St. Helena, 

 which rise abruptly out of the water, are merely the peaks 

 of lofty mountains whose foundations are several miles be- 

 neath the surface of the waves. Not many years ago it 

 was the universal belief that no living animal could exist 

 beyond a depth of a few hundred fathoms ; the ocean at 

 greater depths being supposed to be as destitute of life as 

 the highest mountain-peaks or the sandiest deserts. Deep- 

 sea dredging has, however, shown that life can and does 

 exist at all depths, in greater or less abundance ; the deni- 

 zens of this great deep having undergone modification in 

 order to suit them for living under such peculiar conditions. 

 Thus there is a shark-fishery carried on in Setubal Bay, ofi" 

 the coast of Portugal, where the sharks are often brought 

 up on the lines from a depth of 3000 feet ; but it is found 

 that on reaching the surface they are invariably dead, 

 owing, no doubt, to the removal of the enormous pressure 

 of water under which they are accustomed to live, and 

 without which they can no longer exist. 



A wonderful instrument is the dredge, to which we owe 

 so much information on these matters ; and the sinking 

 and raising of it in deep seas is by no means the simple 



