floor, we use the age-old technique of dredging and the modern 

 technique of coring. To dredge for loose rocks and boulders we 

 simply tow a large steel-framed wire-mesh bag on the end of 

 several miles of cable. The great difficulty lies in trying to find out 

 whether the dredge is dragging along the bottom, or skimming 

 just above it; frequently we come up with only an empty bag. 

 However, some very successful hauls have been made from depths 

 of nearly three thousand fathoms and have given the geologists 

 good specimens to examine. 



We get samples of the soft sediments by driving a long, hollow 

 tube into the bottom. When the tube, called a corer, is brought up, 

 the soft core of sediments — sometimes up to a hundred feet long — 

 gives us a geological and biological record ranging over the past 

 few million years, when the sediments were being laid down. 



The sediments tell only part of the story of the sea floor. To 



Left: Fifty pounds of TNT are exploded 

 in ttie Arctic ice. Seismic surveying of 

 ttiis t<ind reveais not only ttie thickness 

 of ttie ice and ttie deptti of ttie sea floor, 

 but also ttie nature of rocks making up the 

 sea bed (see diagram on opposite page) . 

 Right: A piston coring tube is prepared 

 for its journey to the sea floor where it 

 will cut its way into the sediment layers 

 and withdraw a sample of ocean bottom 

 deposits, some of which were laid down 

 millions of years ago. 



'93 



