362 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 



apparent exception, is probably a case of recent change in the char- 

 acter of the deposit, for the evidence of manganese nodnles and 

 sharks' teeth brought up with this clay is conclusive as to the slow rate 

 of its collection. Readers of Sir John Murray's and Professor 

 Renard's rejDort will remember many cases where recent change in the 

 character of a deposit is to be inferred. 



A point of much importance in connection with our views on 

 oceanic radio-activity is that of the presence in the waters and in the 

 deposits of the parent radio-active substance, uranium. The evi- 

 dence that the full equivalent amount of uranium is present is, I be- 

 lieve, conclusive. 



In the first place, to so vast a reservoir as the ocean the rivers can 

 not be supposed to supply the radium sufficiently fast to make good 

 the decay. In a very few thousand years, in the absence of uranium, 

 the rivers must necessarily renew almost the entire amount of radium 

 present. I have made examination of the water of one gi^eat river 

 onl}^ — the Nile. The quantity of radium detected was 0.0042X10"^- 

 per cubic centimeter. That is less than the oceanic amount. In 

 short, it is evident that the uranium must accumulate year by year 

 in the oceanic reservoir, like other substances brought in by the 

 rivers, and that the present state of the waters is the result of such 

 actions j)rolonged over geological time. 



While this reasoning is conclusive as regards the waters of the 

 ocean, it does not assure us that the sediments accumulating in their 

 depths are throughout as radio-active as their surface parts would in- 

 dicate. There might be a precipitation of radium unattended by 

 uranium, in which case their deeper parts would not be radio-active. 



Against this possibility there is the evidence of such true deep-sea 

 deposits as were formed in past times and to-day still preserve their 

 radio-activity. For instance, the chalk, which, considering that it 

 was undoubtedly a very rapidly formed deposit, exhibits a radio- 

 activity quite comparable with that of the Globigerina oozes, deposits 

 which it most nearly resembles. In this deposit, clearly, the uranium 

 must have collected along with the calcareous materials. "We can 

 with security argue that the similar oozes collected to-day must 

 likewise contain uranium. In the case of the red clays we have the 

 direct determination of the uranium which Prof. Emil Werner was 

 so good as to make at my request. Considering the difficulties attend- 

 ing its separation, the result must be taken as supporting the view 

 that here, too, the radium is renewed from the uranium. Regarding 

 the efforts of other observers to detect uranium in such deposits, it is 

 noteworthy that without the guidance of the radium, enabling spe- 

 cially rich materials to be selected for analysis, the success of the in- 

 vestigation must have been doubtful. The material used was a red 

 clay with the relatively large quantity of 54.4 million millionths of a 



