740 



SCIENCE 



[N. S. Vol. XXVIII. No. 726 



ably, and yet the final results prove sucli 

 as, I believe, can not be ignored. Indeed, 

 those who are in the way of making such 

 calculations, and who enter into the ques- 

 tion, will find that my assumptions are not 

 specially favorable, but are, in fact, made 

 on quite independent grounds. Again, a 

 certain class of effects has been entirely left 

 out of account, effects which will go towards 

 enhancing, and in some cases greatly en- 

 hancing, the radio-thermal activity. I refer 

 to the thickening of the crust arising from 

 tangential pressure, and, at a later stage, 

 the piling up and overthrusting of moun- 

 tain-building materials. In such cases the 

 temperature of the deeper parts of the 

 thickened mass must still further rise under 

 the influence of the contained radium. 

 These effects only take place, indeed, after 

 yielding has commenced, but they add to 

 the element of instability which the pres- 

 ence of the accumulated radio-active de- 

 posits occasions, and doubtless increase 

 thermal metamorphic actions in the deeper 

 sediments, and result in the refusion of 

 rocks in the upper part of the crust." 



The effect of accumulated sediment is 

 thus necessarily a reduction in the thick- 

 ness of that part of the upper crust which 

 is capable of resisting a compressive stress. 

 Over the area of sedimentation, and more 

 especially along the deepest line of syn- 

 clinal depression, the crust of the globe for 

 a period assumes the properties belonging 

 to an earlier age, yielding up some of the 

 rigidity which was the slow inheritance of 

 secular cooling. Along this area of weak- 

 ness—from its mode of formation generally 



"Professor C. Schmidt (Basel) has recently 

 given reasons for the view that the Mesozoic 

 schists of the Simplon at the period of their fold- 

 ing were probably from 15,000 to 20,000 meters 

 beneath the surface {Ee. Geol. HelvetitE, Vol. IX., 

 No. 4, p. 590). As another instance consider the 

 compression of the Laramide range (Dawson, Bull. 

 Geol. Soc. Am., XII., p. 87). 



much elongated in form— the stressed crust 

 for many hundreds, perhaps thousands, of 

 miles finds relief, and flexure takes place 

 in the only possible direction; that is, on 

 the whole upwards. In this way the pro- 

 longed anticline bearing upwards on its 

 crest the whole mass of deposits is formed, 

 and so are born the mountain ranges in all 

 their diversity of form and structure. 



We have in these effects an intervention 

 of radium in the dynamics of the earth's 

 crust, which must have influenced the en- 

 tire history of our globe, and which, I 

 believe, affords a key to the instability of 

 the crust. For after the events of moun- 

 tain-building are accomplished, stability is 

 not attained, but in presence of the forces 

 of denudation the whole sequence of events 

 has to commence over again. Every fresh 

 accession of snow to the firn, every passing 

 cloud contributing its small addition to the 

 torrent, assists to spread out once more on 

 the floor of the ocean the heat-producing 

 substance. With this rhythmic succession 

 of events appear bound up those positive or 

 negative movements of the strand which 

 cover and uncover the continents, and have 

 swayed the entire course of evolution of 

 terrestrial life. 



Oceanic Deposits.— The displacements of 

 the crust which we have been considering 

 are now known to be by no means confined 

 to the oceanic margins. The evidence 

 seems conclusive that long-continued move- 

 ments have been in progress over certain 

 areas of the sea floor, attended with the 

 formation of those numerous volcanic cones 

 upon which the coral island finds founda- 

 tion. Here there are plainly revealed signs 

 of instability and yielding of the crust 

 (although, perhaps, of minor intensity) 

 such as are associated with the greater 

 movements which terminate in mountain- 

 building. I think it will be found, when 

 the facts are considered, that we have here 



