CAUSE OF BASAL DIASTROPHISM 205 



It will help to clarify thought on the subject if we distinguish between 

 the leading part played by heat as the chief opponent of shrinkage in a 

 gaseo-molten earth and the secondary part it plays in a planetesimal earth 

 as merely the product of compression. In a gaseo-molten earth heat is 

 the main agent that stands in the way of further immediate collapse; it 

 must be dissipated before shrinkage will go further. The old masters 

 were, therefore, quite logical in regarding cooling as the chief prerequi- 

 site to shrinkage and deformation; hence cooling seemed to be the chief 

 cause, whereas it was merely the removal of the hindering agency. But, 

 in a body built up of heterogeneous clastic matter at relatively low tem- 

 peratures, it was at first the solid form of the particles that stood in the 

 way of their collapse; later it was the lack of the most dense chemical 

 combination and physical organization that stood in the way. Heat was 

 thus only one of a group of restraining agencies; it is not even the lead- 

 ing one in the order of action. The polarized forces of the solid state had 

 to be overcome and heat produced by compression before it came into 

 action to aid in restraining further compression. This, of course, applies 

 to the heat mechanically produced rather than that which may arise from 

 chemical action of radioactivity. When heat is thus produced mechan- 

 ically it becomes a cooperating factor of notable imj^ortance ; it may come 

 to be a leading one, or even the chief one. But, normally, as the heat 

 rises, some part of it is likely to be consumed in endothermal reactions, 

 some in liquefaction, some in crystalline organization, and some in min- 

 eralogical and other forms of physical reorganization. In so far as any 

 part of the substances engaged in these complex processes takes a mobile 

 form, gravitative pressure, aided by tidal, nutational, rotational, and 

 other forces which were more or less constantly or rhythmically working 

 concurrently Math it, tended to force the mobilized products into higher 

 and cooler zones. They thus mechanically disposed of that part of the 

 heat which produced weakness in the interior, and in that way helped to 

 preserve its rigidity. There is evidence that this restrained the interior 

 action to the limit of insipient liquefaction on the borders of the solid 

 state. In so far as the heat arose from radioactivity, the source is likely 

 to be carried out with its products. A combination of this sort should 

 naturally work toward an equilibrium status between the processes that 

 tended in opi^osite directions, and this equilibrium status should have for 

 its l)oundary line the fusion-solution curve. This automatically sepa- 

 rated the matter that was rigid enough to hold its place and do its part 

 in maintaining the rigidity of the earth, and the weak yielding part that 

 had to go practically as fast as it arose. In the nature of the case, the 

 equilibrium status — and its determinant on the liquid side, the fusion- 



