682 TRANSACTIONS OF SECTION C. 



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 indicate. 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 Professor Emil Werner was so good as to make at my 

 request. Con.sidering the difficulties attending 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, er.abling 

 specially rich materials to be selected for analysis, the success of the investigation 

 must have been doubtful. The material used was a Ked Clay with the relatively 

 large quantity of 64*4 billionths of a gram per gram. In a few grams of this 

 Werner obtained up to seven-twelfths of the total theoretic amount, and ofcour.se 

 the separation of the uranium is not likely to have been complete. 



It might be thought a hopeless task to offer any estimate of the total bulk of 

 the sub-oceanic deposits, and from this to arrive at some idea of the quantity 

 of radium therein contained. Nevertheless, such an estimate is not only possible 

 but is based on deductions which possess considerable security. As a major limit 

 I believe the estimate of the total mass of depo.'^it is unassailable, and such deduc- 

 tions as might be applied will still leave it an approximation to the truth. 



The elements of the problem are simple enough ; we know that the eedimen-i 

 tary rocks have been derived from the ijineous, some ^0 per cent, of the latter! 

 entering into solution in the process of conversion. Some of the soluble con- 

 stituents, owing to their great solubility, have remained in solution since they 

 entered the ocean.^ These are the salts of sodium. An estimate of the amount of 

 these salts in the oceau gives us a clue to the total amount of rock substauce whicii 

 has contributed to oceanic salts and oceanic deposits since the inception of the oceans. 

 Some years ago I deduced on this basis that the igceous rocks which are parent to 

 the sodium in the sea must have amounted to about 91 x 10" tons.- This figure 

 in no way involves the rate of supply by the rivers, or our estimate of geological 

 time. It only involves the quantity of sodium now in the ocean — a fairly well-known 

 factor — and the loss of this element, which occurs when average igneous rocks are 

 degraded into sedimentary rocks — a factor also fairly well known. Mr. F. W. 

 (Hark, to whom geological science is indebted for so much e.xact investigation, has 

 recently repeated this calculation, using data deduced anew by himself, and arrives 

 at the result that the bulk of the parent igneous rock was 843 x 10* cubic miles.* 

 On a specific gravity of 2'6 my estimate in tons gives nearly the same result: 

 84 X 10' cubic miles. 



Now about one-third part of this parent rock goes into solution when break- 

 ing up into a detrital sediment. The limestones upon the land are part of what 

 was once so brought into solution. Having made deduction of these former 

 marine deposits (and I here avail myself of Van Hise's and Clark's estimates of 

 the total amount of the tedimentaries and the fraction of these which are cal- 

 careous),* and, allowing for the quantity remaining in solution in the ocean, the 

 result leaves us with the approximation of twenty million cubic miles of mutter 

 once in solution, and now for the greater part existing as precipitated or abstracted 

 deposits at the bottom of the ocean. We are to distribute this quantity over its 



' Traiu. Boyal Dvbliii Soc, vol. vii. ser. ii. p. 23 ct scq. " Ibid., p. 46. 



» The Data of Geoclievmtry. J3y f. \V. Qlark, p. gi), « Jhid., p, 3]. 



