GEOLOGY. 373 



In such reconsideration, precipitation from a mutual solution should 

 replace surface refrigeration from a supposed melt, since it is well 

 estabUshed that magmas are to be regarded as mutual solutions 

 rather than melts. The main line of the core-forming process must 

 have lain in the formation of crystals or concretions by supersaturation 

 in connection with chemical reactions. WTiile the genetic phases of 

 petrological science have not yet reached a stage that permits an 

 altogether confident opinion as to just how precipitation would proceed 

 in the deep portions of such a mutual solution, it may be safely assumed 

 that the gyratory ckculation due to the rotation of the body would 

 affect both the precipitation and the lodgment of the precipitates. 

 The solid nucleus formed under the shaping influence of such a gyratory 

 cu'culation would certainly not be strictly spherical and could hardly 

 be symmetrically spheroidal; it would depart from these in ways that 

 adapted it to the conditions of precipitation and lodgment along the 

 current courses. 



The importance of this consideration Hes in the obvious fact that 

 any solid core formed at the center of the earth would be the foundation 

 on which the whole overlying portion of the solid globe would be built, 

 and hence it must influence all the subsequent diastrophism. As 

 already noted, the comparison of the earth with its neighbors brought 

 out the very significant conclusion that the high densities of the larger 

 bodies were due mainly to the mass-effect of the later additions. 

 These later additions do not in themselves appear to be specially 

 dense, but rather the opposite. Hence it is logical to conclude that the 

 increased density of the more massive bodies was chiefly due to pro- 

 gressive compression, selective removal, readjustment, and reorganiza- 

 tion of material in the deeper horizons as the bodies grew. Since, then, 

 the core was the part most to suffer this compression and readjustment 

 of material, its specific shape and structure as first formed are matters 

 of no Uttle importance. While the present status of petrology requires 

 reserve in forming a precise picture of the formation of the sohd core 

 from the magma, it is clear that the method of precipitation and lodg- 

 ment of the precipitates must be worked out on the basis of a mutual 

 solution stirred by a gyratory circulation rather than the old notion 

 of the superficial freezing of a quiescent melt. 



IV. The Differential Stresses under which the Formative Processes Took Place. 



The group of stresses that arose from changes in the rate of rotation, 

 from tides, from nutational forces, and other sources, brought to bear 

 upon the forming earth-core conditions that could scarcely fail to 

 influence rather radically its development. Those that take the form 

 of zonal harmonics of the second order may be regarded as representing 

 all general stresses from without. These give rise to strains that 

 assume the form of bulged equators and flattened poles, as in rotational 

 deformations, or the form of polar cones embracing a depressed equator 



