UKANIUM AND GEOLOGY — JOLY. 383 



mighty influences of denudation and deposition are forever at work. 

 And so, perchance, in some remote age the vanished Gondwana Land, 

 the lost Atlantis, may once again arise, the seeds of resurrection even 

 now being sown upon their graves from the endless harvests of pelagic 

 life. 



Appendix A. 

 Convcctive movement of uranium to the earth's surface {p. 359). 



The estimate of temperature siven assumes (1) that the mass of igneous 

 material is spherical, and (2) that its surface is kept at constant temperature, 

 heat escaping freely. The first assumption is in favor of increasing the esti- 

 mate of temperature, and probably would not generally be true, especially of a 

 mass moving upward. The second assumption tends to give a lower estimate 

 of temperature, and is certainly inaccurate, as the surrounding materials are 

 nonconducting and must favor the accumulation of radio-active heat. 



On assumptions (1) and (2) and on Barus's results for the thermal expansion 

 of diabase between 1,100° and IjSOO",*^ and results of my own on basalt,'' which 

 are in approximate agreement, and assuming the mean excess of temperature 

 to be 500° and the surrounding material to be at a fluid temperature, the force 

 of buoyancy comes out at over GO dynes per cubic centimeter of the spherical 

 mass. This is an underestimate. 



If we may assume that the Deccan Trap is indeed an instance of such an 

 overheated mass escaping at the surface, and that similar radio-active masses 

 rising up from beneath at various times in the past may have affected the crust, 

 we have at our disposal a local source of enei'gy of plutonic origin which may 

 account for much. 



Appendix B. 

 Sedimentation and rise of geotherms (p. 378). 



The depth of the upper radio-active layer is, of course, unknown. We pos- 

 sess, however, the means of arriving at some idea of what it must be. The 

 quantitative thermal conditions impose a major limit to its average thickness, 

 and the indications of injected rocks suggest a minor limit. 



If 2.G X 10'" calories is the heat output of the whole earth per annum, and 

 if we assign only one-fifth of this amount to cooling due to decay of the uranium, 

 then, on the assumption that the earth is no longer losing any part of its original 

 store of heat, we have about 2 X lO""* representing radium heating. From this 

 the allowance of terrestrial radium per square centimeter inward is 2.3 X 10-^ 

 grams. This would give a major limit. But it is probable that a large part 

 of this radium is located in more deeply seated parts of the earth. If we take 

 10-^ as contained in the normal radio-active surface layer, and assume (what 

 according to my experiments should not be far from the truth) that the aver- 

 age radio-activity is 3, we arrive at a thickness of 12 kilometers. 



Some such mean value is necessitated by the evidence we derive from the 

 radio-activity of igneous rocks. These rocks must in many cases be derived 



« Phil. Mag., Vol. XXXV, p. 173. 



^ Trans. Roy. Dublin Soc, Vol. VI, p. 298. 



