408 Jones — Review of Chamberlin's Groundwork 



of that recorded would seem to be unnecessary. But then 

 with the prior assumption of a crystalline heterogeneous 

 earth it becomes necessary, of course, to further assume 

 a very great and deep-seated diastrophism of long dura- 

 tion. Daly has clearly shown 35 that simple cooling may 

 be far less effective in volume change than that due to 

 changes in state, both from liquid to solid and from one 

 solid form to another as a result of static metamorphism. 

 These changes together with contraction due to secular 

 cooling would, it seems, be amply sufficient to cause all 

 the lateral deformation of which we have record. 



The actual total circumferential shortening of the earth 

 since Proterozoic time, as recorded on any great circle, 

 is not over 200 miles and is probably nearer 100 miles. 

 If it is 150 miles the total radial shrinkage is then about 

 24 miles. The amount of shortening and shrinkage that 

 can be allotted to pre-Paleozoic time is, of course, indefi- 

 nite. It may not be as much as is generally supposed. 

 Structural deformation of at least Proterozoic terranes 

 is not generally excessive and the Archean rocks are 

 largely igneous, bespeaking great magmatic engulfment 

 and intrusion. Magmatic engulfment and intrusion on 

 such a large scale may well be potent factors in them- 

 selves in lateral deformation. Where these pre-Pale- 

 ozoic terranes do show isoclinal folding they have usually 

 been involved in later deformation. At least their close 

 association with belts of later folding is significant. 



If the earth has suffered any such radial shrinkage as 

 700 miles, as deduced by Chamberlin by the hazardous 

 method of density mass comparisons as between the earth 

 and its nearby neighbors, 36 then a major part of this 

 shrinkage was taken up during the period of growth and 

 the resulting diastrophic record lies in depths forever 

 hidden from view. 



If now diastrophism is the expression of deep-seated 

 inner reorganization due to condensation upon mass 

 increase, what is to provide the diastrophic energies after 

 the cessation of growth! Are we to conclude that this 

 inner reorganization in favor of greater density is to 

 continue without additional mass increase? Either way 

 these questions are answered, it would seem that diastro- 



35 E. A. Daly : Igneous Eocks and their Origin, New York, 1914, p. 176. 



36 Jour. Geology, vol. 29, p. 400, 1921. 



