216 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



cals; also the metals such as manganese and iron, which are often 

 found in gi-eat concentrations, or those which are found in extremely 

 small concentrations, such as coj^per, tin, gold, selenium, or radium. 

 The radium is of particular interest and significance because its con- 

 centration in ocean-bottom sediments has recently been found to be, in 

 general, much greater than in either igneous or sedimentary rocks on 

 land, and this difference is as yet not completely explained. The con- 

 centration is greatest in those portions of the ocean bottom more re- 

 mote from land and lying at the greater depths. The material at the 

 bottom of the deeper parts of the ocean generally consists of so-called 

 red clay, and this material appears to contain much more radium than 

 any rocks yet examined on land. If these sediments are of consider- 

 able depth, and if this radium concentration is the same throughout, 

 these deeps constitute local concentrations of radioactive material 

 possessing enormous stores of energy. Since we have found no sedi- 

 mentary rocks with radium concentrations remotely approaching 

 those existing in these sediments it might be inferred that the many 

 changes of level of various parts of the earth's surface have nowhere 

 brought up an ocean deep. It may be that the deeper portions of the 

 ocean are permanent features of the earth, or else it may be inferred 

 that this high radioactivity is but a transitory thing, representing 

 the activity of radium only, unassociated with its long-lived parent 

 substance uranium. If this be so, the nature and cause of its separa- 

 tion and concentration from sea water would be a most important 

 study. Furthermore, a study of the radioactive substances and their 

 disintegration products in these cores holds a promise of a determina- 

 tion of the time intervals represented by the various strata, or the 

 age of the sediment as a whole. This in itself is of the utmost geo- 

 physical and oceanographic significance. 



The only record of the history of the existing ocean lies buried in 

 its bottom. Whether this record will be easy or difficult to deciphei', 

 voluminous or meager, remains to be ascertained, but whatever its 

 nature it is now accessible to us through the medium of these core 

 samples. 



