ELASTIC STRAIN 311 



Such action need not be complete. Indeed, some excess of mass is found 

 in some elevated areas. 



Of course, if it be granted that significant local variation in the depth 

 of flotational equilibrium is possible, then no such adjustments or density 

 changes need by hypothesized, for the compressed prisms could then float 

 for a time, possibly a long time, lower as well as higher than before their 

 compression. 



But it is to be noted that the action above hypothesized need not violate 

 the principle of isostasy in any significant degree; for with the upfolding 

 there would be incipient arching, incipient relief of pressure beneath the 

 arching area, incipient expansion, and possibly even incipient melting 

 from relief of pressure. These tendencies would go hand in hand simul- 

 taneously at all stages of the process of relief of widespread strain by 

 localized deformation. And the tendency to expansion beneath the fold- 

 ing region would be augmented by the heat generated mechanically in 

 the process of deformation, and by the upward movement of the isogeo- 

 therms beneath the upwarping area. Thus might come about the neces- 

 sary decrease in the average density of the columns whose surface parts 

 had been elevated under the operation of tangential pressure supplied by 

 widespread elastic strain. 



To discuss all this thoroughly, and present a complete hypothetical 

 picture of it, alone would require a book. All that is possible here is a 

 mere outline of the idea that lateral strength combined with vertical 

 weakness in a surficial spherical shell reposing upon, confining, and load- 

 ing isostatically a globular interior the outer part of which may yield and 

 conform, under excess pressure, to movements or changes of shape in the 

 shell may make it possible to harmonize and adjust differences in opinion 

 concerning the interpretation of patent geologic and geodetic findings. 



Here favorable reference must be made to much of what T. Mellard 

 Eeade 10 wrote concerning the origin of mountains, though without ac- 

 ceptance here of his primary thesis. In past and present mountain re- 

 gions many batholiths have melted, risen, cooled and crystallized with 

 accompanying volume and density changes; and, as Eeade pointed out, 

 and this is thoroughly consistent with the operation of the principle of 

 isostasy, the only direction for relief of the stresses induced by such 

 changes is the vertical. These changes appear to the writer to be con- 

 sistent and expectable concomitants of incipient relief by incipient arch- 

 ing as the result of tangential pressure and the train of consequences of 

 this. It seems also to the writer that such a combination of tangential 

 pressure with vertical expansion and upward movement, surely involving 



