52 THE OCEAN FLOOR 



what conclusions deep-sea chronology has contributed 

 will be described below. Here, as an introduction, I 

 shall summarize what we know about the total thickness 

 of the sediment carpet and its substratum, the rock bed 

 of the ocean floor. 



By theoretical reasoning various authors have tried 

 to estimate the amount of sediment accumulated on the 

 deep-sea floor since the birth of the oceans, assumed to 

 have taken place between two and three billion years 

 ago. As a basis for these speculations general geochem- 

 ical considerations have served, notably the quantities 

 of debris carried oceanward from rocks which have 

 eroded on the continents. Out of such debris certain 

 components have remained in solution, whereas others 

 have reached the sediments on the ocean floor. The 

 conclusions drawn from these calculations have been 

 variable, ranging from a few hundred feet to over 70,- 

 000 feet. As a result of most painstaking work, Philipp 

 Kuenen of Groningen in Holland, one of the leading 

 European authorities on submarine geology, has worked 

 out theoretical average thicknesses of pelagic ocean 

 sediments. According to Kuenen the average thickness 

 of deep-sea sediments should be about 3 kilometers. 

 For red clay, which has the lowest rate of sedimentation, 

 he found 2.2 kilometers, or over 7,000 feet, to be the 

 most probable average thickness.^ 



If we ascribe to the time of accumulation a total 

 length of two billion years, Kuenen's figures would 

 necessitate an average rate of sedimentation for red 



