GEOLOGY. 425 



earth. This would hold even if all compressive energy is reckoned as 

 heat, which is not realized in fact. The actual gradient of tempera- 

 ture is notably steeper than the computed compressional temperature- 

 curve. The actual temperature, therefore, is assigned, under the 

 planetesimal hji^othesis, to the ascent of magmas from below. There 

 is thus reduction of heat below and gain of heat above, an equalizing 

 thermal process. The powerful extrusive agencies of a solid globe 

 are assumed to force practically all mobile matter outward into the 

 cool surficial zone, whether made mobile at shallower or deeper depths. 

 Liquefaction is thus made a persistent auxiliary of the compressive 

 process. 



The extrusion involves a suggestive chain of transformations of the 

 compressional energy. The liquefaction in the depths involved the 

 transformation of thermal energy into a phase which reduced rigidity 

 and increased mobility. The mobile masses, in passing to higher 

 horizons, exchanged heat, and perhaps exchanged substance, along 

 their routes and increased their potential energy by their ascent. 

 This, however, was offset by the descent of equivalent matter in the 

 solid mass that forced the liquids up. In the cool zone the magma 

 gave up heat which raised the regional temperature and contributed 

 to the temperature gradients of the outer shell. By the solidification 

 of the magmas thus squeezed outward, and by the pyro-clastic and the 

 sedimentary derivatives from them — aided still somewhat by acces- 

 sions from without — the outer shell was built up. The structure thus 

 given it is really distinctive and requires such a revised interpreta-> 

 tion as this to bring out its significance. It seems to be out of accord 

 with the holomolten hypothesis. Its dominant feature is given by the 

 necks and dikes that mark the magmatic ascents, the stocks, bulbs, and 

 batholitic masses that mark the lodgment of magmas in the cooling 

 zone, and the sheets and streams of overflow that mark the expansion 

 and spread of lavas on the surface. From these, as feeding sources, 

 the derivatives took their origins and had their special distributions. 

 No remnants of primitive crust bearing the characteristics assignable 

 to a holo-molten globe are in evidence. The observed temperatures 

 have varying irregular features primarily assignable to the long series 

 of igneous intrusions that built the outer shell, and secondarily to the 

 earth's compression and the resulting metamorphisms and diastro- 

 phisms. The temperature gradients, like the density gradients, carry 

 their own credentials in the form of peculiarities assignable to the spe- 

 cial modes of their origins. The study of these is the next in order. 



