September io, 1908] 



vVy^ TURE 



459 



success of the investigation must have been doubtlul. The 

 material used was a Red Clay with the relatively large 

 quantity of 544 biUionths of a gram per gram. In a few 

 grams of this Werner obtained up to seven-twelfths of the 

 total theoretic amount, and of course 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 con- 

 siderable security. As a major limit I believe the estimate 

 of the total mass of deposit is unassailable, and such deduc- 

 tions as might be applied will still leave it an approxima- 

 tion to the truth. 



The elements of the problem are simple enough ; we 

 know that the sedimentary rocks have been derived from 

 the igneous, some 30 per cent, of the latter entering into 

 solution in the process of conversion. Some of the soluble 

 constituents, 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 ocean gives us a clue to the total amount of rock 

 substance which has contributed to oceanic salts and oceanic 

 deposits sinci the inception of the oceans. Some years ago 

 I deduced on this basis tliat the igneous rocks which are 

 parent to the sodium in the sea must have amounted to 

 about 91 X to"* 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. Clark, to whom geological science is 

 indebted for so much exact investigation, has recently re- 

 peated this calculation, using data deduced anew by him- 

 self, and arrives at the result that the bulk of the parent 

 igneous rock was 84-3x10' 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 breaking 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 1 here avail myself of Van 

 Hise's and Clark's estimates of the total amount of the 

 sedimentaries 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 matter 

 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 floor. 

 If the rate of collection had been uniform in every part 

 of the ocean throughout geological time, a depth of about 

 one-seventh of a mile (240 metres) of deposit would cover 

 the ocean bed. 



While, I believe, we can place considerable reliance on 

 this approximation, we are less sure when we attempt 

 an estimate of its mean radio-activity. If we assume for 

 it an average radio-activity similar to that of Globigerina 

 Ooze, we find that the quantity of radium involved must 

 be considerably more than a million tons. Apart from 

 the value which such estimates possess as presenting us 

 with a perspective view of the great phenomena we are 

 dealing with, it will now be seen that it supports the find- 

 ing of the experiments on sedimentary rocks, and leads 

 us to anticipate a real difference in the radio-activity of 

 the two classes of material. 



The Sedimentary Rocks. — The radium content of those 

 of detrital character is indicated in the following sand- 

 stones, slates, and shales : — 



Shales, sandstones, grits (10) 4'4 



Slatfs (Cambrian, Devonian) 47 



Mud from Amazon ':-2 



Some of the above are from deep borings in Carbon- 



1 Trans. Royal Dublin Soc , vol. vii., ser. ii., p. 23 vi st'</. 

 - Ibid.^ p. 46. 



3 " The Data of Geochemistry," by F. W. Clark, p. 20. 

 i lbid.,f.-i,. 



NO. 2028, VOL. 78] 



iferous rocks (the Balfour and Burnlip bores),' and from 

 their nature, where not actually of fresh-water origin, can 

 owe little to oceanic radio-activity. Many of the following 

 belong to the class of precipitates, and therefore owe their 

 uranium wholly or in part to oceanic source : — 



Marsupites chalk 4'2 



Green sandstone 4'9 



Green sand (dredged) 4 5 



Limestones and dolomites [Trenton, Carboni- 

 ferous, Zechstein, Lias, Solenhofen (7)] 41 



Keuper gypsum 6 '9 



Coral rock, Funafuti bore (4)- 17 



Trias-Jura sediments, Siniplon : 17 rocks of 



various characters 6 '9 



Mesozoic sediments, St. Gothard : 19 rocks of 



various characters 4'2 



The general mean on sixty-two rocks is 4-7. 



Making some allowance for uncertainties in dealing with 

 the Simplon rocks, I think the experiments may be taken 

 as pointing to the result : — 



Igneous rocks from 5 to 6. 



Sedimentary rocks from 4 to 5. 



If our estimate of oceanic radium be applied to the 

 account of the sedimentary rocks in a manner which will 

 be understood from what I have already endeavoured to 

 convey, there will be found to exist a fair degree of 

 harmony between the great quantities which we have found 

 to be in the sediments of the ocean and the impoverish- 

 ment of the sediments which the e.xperiments appear to 

 indicate. 



In all these results fresh and unweathered material has 

 been used. The sand of the .-Arabian desert gave me but 

 0-4. Similarly low results have been found by others for 

 soils and such materials. These are not to be included 

 when we seek the radio-activity of the rocks. 



.-\s regards generally my experiments on the radium- 

 content of the rocks, I cannot say with confidence that 

 there is anything to indicate a definite falling off in radio- 

 activity ill the more deeply seated materials I have dealt 

 with. The central St. Gothard and certain parts of the 

 Deccan have given results in favour of such a decrease. 

 On the other hand, as will be seen later, the granite at 

 the north end of the St. Gothard and the primitive gneiss 

 of the Simplon show no diminution. According to the 

 view I have put forward above as to the origin of the 

 surface richness In radium it is, I think, to be expected 

 that, while the richest materials would probably rise most 

 nearly to the surface, there might be considerable variability 

 in the radio-activity of the deeper parts of the upper crust. 



Uranium and the Internal Heat of the Earth. 



While forced to deny of the earth's interior any such 

 richness in radium as prevails near the surface, the infer- 

 ence that uranium exists yet in small quantities far down 

 in the materials of the globe is highly probable. This view 

 is supported by the presence of radium in meteoric sub- 

 stances and by its very probable presence in the sun — that 

 greatest of meteorites. True, the radio-thermal theory 

 cannot be supposed to account for any great part of solar 

 heat unless we are prepared to believe that a very large 

 percentage of uranium can be present in the sun, and yet 

 yield but feeble spectroscopic evidence of its existence. 

 Taken all together, the case stands thus as regards the 

 earth. We are assured of radium as a widely distributed 

 surface material, and to such depths as we can penetrate. 

 By inference from the presence of radium in meteoric sub- 

 stances and its very probable presence in the sun, from 

 which the whole of terrestrial stuff probably originated, 

 as well as by the inherent lil-celihood that every element 

 at the surface is in some measure distributed throughout 

 the entire mass, we arrive at the conclusion that radium 

 is indeed a universal terrestrial constituent. 



The dependent question then confronts us — Are we living 

 on a world heated throughout by radio-thermal actions? 

 This question — one of the most interesting which has 



1 For these rocks, and for much other valuable material, I have to thank 

 Mr. D. Tate, of the Scottish Geological Survey. 



- For these I have to thank the Trustees of the British Museum and 

 Mr. .\. S. Woodward, F.R.S. 



