12 C. R. VAN HISE 



contraction due to secular cooling is mainly confined to the 

 outer 200 or 300 miles of the earth, and states: "Although no 

 estimate can be made of the contraction of this portion, it is 

 probably safe to say that its volume cannot have been diminished 

 so much as one-tenth ; and if we were to assign thirty miles as 

 the diminution of the earth's radius since the formation of a 

 cooled exterior, we should probably reach the utmost limits 

 consistent with Fourier's theorem." 



It is believed, upon the one hand, that there may have been 

 great overestimates of the amount of crustal shortening, and 

 upon the other hand, that important causes for nucleal con- 

 traction may exist which have not been sufficiently considered. 

 It is the purpose of this paper (1) to examine the evidence upon 

 which estimates of crustal shortening have been made, and to 

 consider the methods to be followed in making estimates of 

 shortening, and (2) to summarize the known causes which may 

 exist for nucleal contraction and crustal corrugation. The paper 

 may thus be divided into two parts. In Part I, I shall consider 

 the shortening of the outer surface of the earth accompanying 

 folding, faulting, jointing, cleavage, fissility, and vulcanism and 

 cementation; and in Part II, I shall consider the causes which 

 may account for the shortening represented by the phenomena. 



PART I. ESTIMATES OF CRUSTAL SHORTENING. 



Folding. — The deformation of folding undoubtedly involves 

 shortening, but it is believed that it does not necessarily require 

 nearly so much shortening as has been believed. Estimates 

 of shortening resulting from folding have not considered the 

 effects of the following phenomena: (1) the thinning of the 

 layers produced by folding; (2) the composite character of 

 folds and the rapid variations in the closeness of the folds of 

 the various orders ; and (3) the effect of gliding on the limbs 

 of folds. 



1. In order to make an estimate of the amount of shortening 

 involved in folding, it is necessary to recall the nature of the 

 deformation of the individual beds and formations. It has been 



