DIASTROPHISM AND THE FORMATIVE PROCESSES 491 



earth and of Venus. But just how far down the scale it held its 

 dominance may best be left an open question for the present. 

 The considerations about to be offered imply that the second line 

 of evolution was preponderant in the history of the small nuclei. 



In nuclei massive enough and quiescent enough to maintain 

 high internal temperatures it seems probable that the precipitates 

 would generally pass from the gaseous state directly into liquid 

 droplets which would serve for a while as Brownian particles and 

 gradually gather into liquid cores, which in turn would develop 

 solid precipitates within themselves and ultimately collect into 

 solid cores. In following this more typical line of gaseous descent, 

 however, it is important to discard the old view that magmas are 

 melts, and to replace it with the modern view, now well established, 

 that magmas are mutual solutions. There are of course melts, and 

 melts sometimes freeze, and so melting and freezing have some place 

 in geological processes, but it is a rather trivial one compared with 

 solidification by chemical processes. Even on the present surface 

 of the earth, which for a hundred millions of years or more has 

 been developing a temperature contrast between the exterior and 

 the interior, simple refrigeration has little expression except in the 

 form of thin crusts; the interiors of even surface lava flows or 

 pools have solidified chiefly by crystallization brought about by 

 saturation in the mutual solution. In a nucleus so conditioned as 

 to sustain the progressive collection of a liquid core at its center 

 by hot precipitates from enshrouding gases there is little ground 

 for postulating even the trivial crust formation that takes place on 

 lavas poured out on the present cold surface. Superficial refrigera- 

 tion could scarcely have been more than a negligible process. 

 Appropriate temperatures and pressures must of course have been 

 very essential factors in core formation, but rather as imperative 

 conditioning influences than as direct agencies. They were less 

 intimate and ultimate factors than the chemical forces that served 

 as the immediate actuating agencies. 



Unfortunately, present knowledge of the precipitating processes 

 deep within magmas is insufficient to predict with much confidence 

 the history of even an ideal liquid core in a perfectly quiescent 

 state, much less to forecast the solidification of a core actuated by 



