OCEANOGRAPHY IN THE UNITED STATES 295 



in sections. We have tlie veiy thin crust, the thick mantle which is 

 about 1,800 miles thick, the outer core, about 800 miles thick, and 

 lately we have found an inner core, and the inner core and outer core 

 are taken to be some mixture of nickel and iron, quite dense, quite 

 heavy, and probably quite hot, about 4,000 degrees centigrade, and 

 magnetic. 



Some of the scientific reasons we want to drill this hole and obtain 

 a sample of the mantle is that everything we see on here has been 

 obtained in an indirect fashion. 



The temperature infonnation perhaps was obtained not quite so 

 indirectly but it was deduced from the surface down to the interior 

 by shallow probes which have been stuck into the ocean bottom and 

 other places on the continents. 



The structure we see here has been obtained from observing earth- 

 quake shock waves as they passed from the point of origin through 

 the crust to the point of observation, by studying the travel times and 

 the velocities of these waves. They have been able to figure out that 

 the earth generally is made up of these various layers. They are 

 really not layers but for lack of a better term we call them layers, these 

 various boundaries which probably grade into each other. 



The densities have been obtained generally from laboratory studies 

 and from making gravity observations around the earth, and the 

 pressures have been deduced lately principally from laboratory ob- 

 seiwations at General Electric. 



We find, then, that everything we know is indirect. What we pro- 

 pose to do is to drill as deeply into this crust, through the crust and 

 as deeply into the mantle as we can, get a sample of the mantle, find 

 out what it is really made of, and we hope to end part of the specu- 

 lation about what the mantle is. 



One of the striking features about the difference between continents 

 and the ocean basins is that in the ocean basins there is no granite. 

 In the continents everywhere you find a large mass of granite which 

 you will see on figure 2 in our prepared statement. 



This means that the granite under continents has bent down the 

 earth's crust, pushing it down through sheer weight, so we cannot 

 possibly hope to reach the mantle under the continents. 



Under the oceans there is no granite. This is the principal dif- 

 ference between ocean basins and the continents. 



We also find under the oceans a thin layer of sediments averaging 

 from 1,000 to 600 feet in thickness. 



Actually we should find a layer of sediments many times that thick. 

 One of the big problems is what happened to all the ages of sedi- 

 ments. There should be an accumulation of about 500 million years 

 of sediments in the oceans. Actually all we can find so far is about 

 100 million years worth of sediments, so there must be somewhere 

 beneath the ocean bottom some sediments. If the sediments are miss- 

 ing then this will give us some reason to think that perhaps the ocean 

 basins are not as old as we think they are. 



We have no idea what the second layer and third layer are com- 

 posed of. Some people say it may be limestone and it also may be 

 basalt. It also may be that there is a high velocity layer of basalt in 

 the second layer which masks everything below it. 



If we find a tremendous thickness of sediments in the basins con- 

 taining a great deal of limestone we will have to then go back and 



