SKCT. 1] 



THE CRXJSTAL ROCKS 



87 



laboratories. There are large areas in which there are no observations. For 

 example, there are no published data on the Arctic Ocean and the South 

 Atlantic, and there are only five stations in the Indian Ocean concentrated in 

 a small region near the equator. 



Present results certainly cannot be regarded as an adequate sample of all 

 oceans. There is still the possibility that some of the areas not yet investigated 

 will differ significantly from the average of those already studied. This is a 

 continuing study, and exploration of many of the open areas is being planned 

 or is in progress. As new data become available, modification of our present 

 ideas about oceanic structure is expected. 



Atlantis-Caryn refraction station 35 August 22, 1950 



^°^y" 35A 

 SW ^^^ 



10 15 20 25 



Direct water wove travel time (sec) 



Atlantis 



Fig. 4. Travel-time plot of Atlantis-Caryn Station 35, southeast of Bermuda. Layer 2 

 velocity = 4.57 km/sec; Layer 3 velocity = 6.54 km/sec; Layer 4 velocity = 8.08 

 km/sec. (After Officer, Ewing and Wuenschel, 1952.) 



Seismic-refraction observations of the oceanic crust have been obtained by 

 investigations at a relatively small number of laboratories. In the United 

 States work has been done by Woods Hole Oceanographic Institution, Lamont 

 Geological Observatory and Scripps Institution of Oceanography ; in England 

 by the Department of Geodesy and Geophysics of the University of Cambridge ; 

 and in the U.S.S.R. by the Institute of Geophysics and the Institute of 

 Oceanology. 



Examples of travel-time plots taken from published work of these labora- 

 tories are illustrated in Figs. 2-8. Fig. 2 represents a radio-sonobuoy station of 



