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would be to drill a hole right through the bed of the ocean and 

 find out. Not only would we learn about the rock floor beneath 

 the carpet of sediments, but we could complete our geological 

 calendar of the sediments themselves, whereas now we have sampled 

 only the top few feet. As this book is being written, engineers are 

 attempting to drill such a hole off the west coast of Mexico (p. 14). 



As we continue our journey along the ocean floor and move 

 toward the center of the Atlantic by crossing fields of sediments 

 undulated by deeply-buried basement rocks, we find that the depth 

 gradually decreases, the bottom becomes rougher, and there are 

 more and more volcanic peaks sticking up through the sediments. 

 Eventually we find ourselves facing an enormous mountain range 

 rising ten thousand feet from the ocean floor, and in places breaking 

 the surface of the water. Such mountain peaks are the Azores in 

 the North Atlantic and the St. Paul's Rocks, Ascension Island, and 

 Tristan da Cunha in the South Atlantic. 



Known in the Atlantic as the mid-Atlantic Ridge, this vast 



The first stage in an attempt to drill a hole 

 through the Earth's crust down to the mantle 

 was carried out in March 1961. The drilling 

 apparatus of the ship shown here penetrated 

 two miles of water, 500 feet of sediments, 

 and 50 feet of rocl<.. The ship was held In 

 position above the drill by signals 

 transmitted by electronic marker buoys. 



Large fractured boulders of pillow lava 

 on a slope of the mid-Atlantic Ridge are 

 shown In this photograph tal^en at a depth 

 of 870 fathoms. The area Illustrated is 

 about six by ten feet. 



197 



