106 THE OCEAN FLOOR 



the primary factor. An important remark made by 

 Revelle in the shipboard report of the "Capricorn" 

 Expedition concerns the deposition on the deep-sea 

 floor of sediments high in calcium: 



If the deposition throughout the geologic past had been like 

 that at the present time it would be impossible to arrive at 

 a geochemical balance, because both the deep-sea and con- 

 tinental sediments would be higher in calcium than the 

 igneous rocks from which they are derived. Thus we arrive 

 at another most important conclusion, namely that the char- 

 acter of the deposition on the deep-sea floor has changed 

 radically with time; throughout most of geologic history, 

 deep-sea sediments must have been lower in calcium than 

 the average igneous rocks, whereas the present deposits 

 have an excess of calcium. 



Some important contributions toward the knowledge 

 of deep-sea sediments from other workers on the 

 "Albatross" material should also be mentioned. 



W. R. Riedel of Adelaide, who worked for two years 

 in Goteborg with the radiolarians from our Pacific and 

 Indian cores, found them useful for dating various 

 sediments.^ This fact is especially important when 

 calcareous components (the foram tests) are missing. 

 Thanks to Riedel's work it is now possible to date with 

 a certain degree of accuracy sediments from the Upper 

 Cretaceous and various Tertiary periods. 



The radiolarians have also proved to be good in- 

 dicators of the transportation and erosion of sediments 

 in the deep sea. Because the tests are more easily kept 



