UEANIUM AND GEOLOGY JOLY. 365 



Igneous rocks from 5 to G. 



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 Avhat 

 I have already endeavored 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 impoverishment of 

 the sediments which the experiments appear to indicate. 



In all these results fresh and unweathered material has been used. 

 The sand of the Arabian desert gave me but OA. Similarly low re- 

 sults have been found by others for soils and such materials. These 

 are not to be included when w^e seek the radio-activity of the rocks. 



As regards generally my experiments on the radium-content of the 

 rocks, I can not say with confidence that there is anj^thing to indicate 

 a definite falling off in radio-activity in the more deeply &eated 

 materials I have dealt with. The central St. Gothard and certain 

 i:)arts of the Deccan have given results in favor 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 ex- 

 pected that while the richest materials w^ould 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. 



"VVliile forced to deny of the earth's interior any such richness in 

 radium as prevails near the surface, the inference that uranium exists 

 yet in small quantities far down in the materials of the globe is highlj'^ 

 probable. This view is supported by the presence of radium in 

 meteoric substances and by its very probable presence in the sun — 

 that greatest of meteorites. True, the radio-thermal theory can not 

 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: \Ye are assured of radium as a widely distributed surface 

 material, and to such depths as w^e can penetrate. By inference from 

 the presence of radium in meteoric substances and its very probable 

 presence in the sun, from which the whole of terrestrial stuff probably 

 originated, as well as by the inherent likelihood 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 ter- 

 restrial constituent. 



