DIASTROPHISM AND THE FORMATIVE PROCESSES 5 



measure, but they are really quite minute when compared with the 

 260,000,000,000 cubic miles of the earth mass. 



It will be noted that this view is a reversal of the old inter- 

 pretation. Instead of being a residual effect of former excessive 

 heat, extrusive igneous action is initiated automatically within the 

 body and forms a regulative system through which the solidity of the 

 globe is maintained. The extrusive action is at the same time 

 merely a minor feature in a general genetic process that has con- 

 served the potential resources of shrinkage and rendered them 

 available at such successive stages in the history of the planet's evo- 

 lution as developed the conditions necessary to call them into action. 



But, notwithstanding the ampler possibilities of shrinkage 

 which this newer view places at the command of students of 

 diastrophism, the pall of restraint has not as yet been wholly lifted. 

 Thus far there has been no well-grounded estimate of the total 

 earth shrinkage that has actually taken place. Even a theoretical 

 estimate of the shrinkage available for interpretative assignment 

 is still lacking. Workers in this field are thus still more or less 

 under the shadow of restraint. Research will certainly proceed 

 with more equipoise if workers can feel wholly untrammeled by 

 supposed limitations in following to their logical conclusions any 

 leadings of evidence they may encounter, even though its demands 

 may be greater than general considerations have thus far seemed 

 to warrant. 



THE SPECIFIC FIELDS THAT YIELD DIASTROPHIC EVIDENCE 



A glance at the field evidences of diastrophism will further pre- 

 pare the way for a study of the probabilities of the case. Diastro- 

 phism is displayed in three great fields. These are closely related,, 

 to be sure, but yet sufficiently different to require individual 

 recognition. 



I. The first embraces the deformations of the distinctly strati- 

 fied terranes, chiefly those of the Paleozoic and later ages. These 

 are relatively accessible, and the constituent formations usually 

 so far retain their individuality as to be susceptible of being satis- 

 factorily traced throughout the whole tract involved in the defor- 

 mation under study. 



