1915-] EARTH FROM THE VIEWPOINT OF GEOLOGY. 283 



A revised view of the nature and location of earth-stresses seems 

 also to be required by what is now known of earth-conditions. 

 Under the former dominance of the tenet of a molten globe, it was 

 natural to assign to the stress-differences of the earth a distinctly 

 superficial localization and limitation ; they were thought to be af- 

 fections of "the crust" almost solely. Hydrostatic pressures were 

 of course recognized as affecting the deep interior, but these were 

 obviously balanced stresses, they were ineffective in deformation. 

 The stresses supposed to give rise to the great reliefs of the earth's 

 surface were thought to be very superficial. But the stresses im- 

 posed by known deformative agencies are not all superficial, nor 

 are their intensities always greatest at the surface. According to 

 Sir George Darwin, the stress-differences generated in the earth by 

 the tidal forces of the moon are eight times as great at the center 

 of the earth as at the surface. So also, according to the same 

 authority, the stresses engendered by changes in the rotation of the 

 earth are eight times as great at the center as at the surface and are 

 graded between center and surface. The tidal stress-differences are 

 relatively feeble but are perpetually renewed in pulsatory fashion. 

 Those that arise from rotation belong to the highest order of com- 

 petency. The stress-difference that would arise at the center of the 

 earth from a stoppage of the earth's rotation, would, according to 

 Darwin, reach 32 tons per square inch. Changes of the rate of rota- 

 tion are almost inevitable when great diastrophic readjustments 

 take place. Such periods are to be regarded as critical times at 

 which great floods of lava should be poured forth from the in- 

 terior if liquid material were there in great volume ready to respond 

 to the changes of capacity which the deformation of the earth's sec- 

 tors and the change in the spheroidal form would inevitably impose. 



Not to detain you with other considerations, the foregoing seem 

 best to comport with an essentially solid state of the earth's interior, 

 if they do not point rather definitely to such a state. Even if they 

 stood alone, they would seem to make a prevaiHng solid state the 

 most tenable working hypothesis. 



But they are far from standing alone ; the geological evidences 

 are strongly supported by considerations that spring from several 

 kindred lines of inquiry. The testimony of astronomic evidence 



