INVESTIGATING THE FLOOR 71 



cerning the velocity of compressional waves in the 

 sedimentary layer. 



Important contributions to this problem have been 

 obtained from the recent "Capricorn" Expedition to the 

 equatorial and southern Pacific Ocean, planned and 

 directed by R. Revelle, director of Scripps Institution 

 of Oceanography. This expedition, which was excel- 

 lently equipped and carried a picked staff of scientists — 

 among others Arrhenius, Riedel, and Rotschi — had the 

 advantage of being composed of two ships which worked 

 together, especially at refraction shootings. The results 

 have been incorporated in a preliminary report, which 

 may be briefly summarized. 



The seismic refraction work carried out during the 

 "Capricorn" Expedition and earlier expeditions in the 

 Pacific Ocean indicates that the thickness of unmeta- 

 morphosed sediments over a large part of the deep 

 Pacific Basin is at most a few hundred meters. Geo- 

 chemical considerations require that the total thickness 

 of deep-sea deposits laid down throughout the geologic 

 past should be five to ten times this figure. From the 

 estimated rate of deposition during and since the 

 Tertiary we find that the observed thickness of sediments 

 corresponds at most to a deposition over one or two 

 bilUon years. We are thus almost forced to the con- 

 clusion that if deposition of sediments was taking place 

 in the deep sea prior to the late Mesozoic, these earlier 

 deposits are not now present in unmetamorphosed form. 



