RADIOACTIVE ELEMENTS AND DEEP-SEA SEDIMENTS 387 



to authigenic minerals and to fossils. Variations in the isotopic 

 composition of lead also present interesting possibilities for study 

 for the future (Chow and Patterson, 1959). 



Conclusions 



In concluding, a comparison should be made with the present 

 state of development of the chronological methods employed in 

 classical geology. Since 1945, the radioactive methods of geo- 

 chronology have undergone spectacular development, especially 

 in the field of pre-Cambrian geology. This successful period was, 

 however, preceded by a static period of nondevelopment, lasting 

 all of forty years. The sudden spurt appears to be due to two 

 causes: (1) the development of new chemical and mass spectro- 

 metrical techniques, and (2) a clearer understanding of the 

 fundamental geochemistry of the elements in question: uranium, 

 lead, rubidium, strontium, etc. 



In the chronology of recent sediments we are for the moment 

 still in the static period. We find ourselves in need of more rapid 

 and more precise methods for the analysis of ionium, protactinium, 

 and thorium. We need a greater number of analyses of sediments 

 and of sea water. But, above all else, we need a knowledge of the 

 fundamental geochemistry of these nuclides. In what chemical 

 form are they present in the ocean? What is the mechanism of 

 their transport to the bottom? What happens to them, once 

 precipitated on the bottom? The list of unanswered questions is 

 too long to be given here. 



I should like to conclude with a remark suggested also by com- 

 parison with work in classical geology. We find that a large number 

 of the results of geochronological researches which were abandoned 

 in the first instance because of the impossibility of interpretation, 

 and which thus appeared to be meaningless, now, in the light of 

 our present knowledge are of much interest. Their interest lies not 

 in the ages which they indicate but in the information as to the 

 mechanism of certain fundamental geological processes such as 

 the formation of granites, metamorphosis, and orogenesis which 

 may be deduced from them. It is equally certain that an important 

 and often unexpected aspect of future research Into the chronology 



