GEOLOGY. 415 



almost ideal conditions for the evolution of volcanic gases when the 

 mixed matter was later subjected to heat and pressure. The moon is 

 especially instructive in this respect, for it was incompetent to hold 

 an atmosphere of hot volcanic gases and the equilibrium quantity 

 was zero. 



6. If the earth was assembled in a fluid state, the radioactive sub- 

 stances should have settled toward the center because of their high 

 specific gravities, or else, if convection prevented this, they should have 

 been distributed subequally throughout the whole mass. But the 

 special students of the subject have shown that if the whole earth were 

 as rich in radioactive matter as its outer part is found to be, the heat 

 generated would be many times greater than that now conducted to 

 the surface and radiated away. Hence the earth should have been 

 growing hotter throughout geological history and no shrinkage at all 

 could be assigned to cooling. On the other hand, if the earth was 

 built up of heterogeneous clastic matter carrying its chance portion of 

 radioactive substances, and if these, by their heating action, led to the 

 liquefaction of the most susceptible matter immediately inclosing them, 

 and if such liquid matter were then forced to or toward the surface by 

 the extrusive forces, the effect would be concentration there, in harmony 

 with the apparent fact. So far as diastrophism is concerned, the con- 

 cept of a molten earth is seriously embarrassed by this newly discovered 

 source of heat added to the heat inherited from condensation. To 

 the concept of a cold solid earth, the liquefying aid of radioactive sub- 

 stances is a welcome cooperating agency. It is obvious that in so far 

 as heat is generated by radioactivity in the crust, the cooling of the 

 earth is prevented and the efficiency of cooling as a deformation 

 agency is reduced, if indeed not forestalled entirely. 



When the foregoing considerations are brought together they seem 

 to show that the resources of energy available for actuating diastro- 

 phism are scant to a serious degree in the older cosmological view of an 

 early gaseo-molten state of the earth, while very much more ample, 

 and seemingly quite adequate, resources of diastrophic energy are 

 available under the accretional view. The subsequent inquiry was 

 mainly confined to the hj^Dothesis that thus shows adequacy. 



The next step in the inquiry was a comparative study of the phases 

 assumed by compressional energy when the body affected is solid and 

 its resistance to compression is such as arises mainly from the prop- 

 erties that give it rigidity and elasticity. 



COMPRESSION IN THE LIGHT OF NEW DISCOVERIES. 



It is important to note at the outset the new aspect the concept of 

 compression takes as the result of the revolution in the concept of 

 matter. So long as atoms were supposed to be irreducible spheres, 

 it was logical to assume that when these were pressed into contact 



