DISTRIBUTION OF THE DEFORMING FORCE 219 



sheets moved in general from high toward low latitudes in both hemi- 

 spheres — that is, both polar areas were regions of crnstal dispersion or 

 spreading, and the continental sheets, excepting Africa, all crept toward 

 the equatorial zone. Hence the general order or plan of deformation 

 was the same for both hemispheres, and the two complementar}^ halves 

 taken together make a symmetrical whole. 



Distribution of the deforming Force 



If the foregoing conception of the manner of production of the Ter- 

 tiary mountain ranges be erroneous it is, of course, useless to seek an 

 explanation of the earth's plan by this means. It may be said, however, 

 for this conception that it is built upon a foundation consisting solely 

 of ol)served facts, without any dependence upon a preconceived idea of 

 the cause of the crustal movements, and yet it reveals, in the distribution 

 of the Tertiary mountain belt and in characters which show the relations 

 of the several parts of that belt to the continental crustal sheets, a degree 

 of systematic order and unity not reached by other methods, and this 

 alone seems to justify further consideration. 



It is worthy of note that no other great crustal movements than those 

 described above appear to have occurred in the Tertiary diastrophism. 

 Indo- Africa was not affected by tangential movement. If it was affected 

 at all it moved only radially — ^that is, either up or down. There ap- 

 pear to be conflicting evidences on this point, but the great rift valleys of 

 the lake region in Africa suggest moderate uplift. These valleys are 

 roughly meridional and suggest a slight girth-expansion of the earth. 

 This effect, however, is relatively small, and for the present purpose is 

 negligible. The tangential movements affecting the other continents 

 may therefore be taken as a substantially complete inventory of Tertiary 

 deformation. 



The facts of distribution seem to show plainly that the deforming 

 forces were in some way conditioned by latitude, for vast crustal sheets 

 moved toward lower latitudes from both poles, and these movements ap- 

 pear to have satisfied largely the stresses caused by the deforming forces. 

 The effect appears to be the same as if the deforming forces had operated 

 to flatten the earth at the poles. If Africa were slightly uplifted without 

 tangential movement, this uplift and the meridional rifting may be an 

 effect of equatorial bulging or girth-expansion. But whether Africa 

 shows equatorial expansion or not, the remainder of the continents surely 

 show polar flattening and crustal dispersion. The deforming force ap- 

 pears to have acted with maximum power in high latitudes, for the 



