302 THOMAS CHROWDER CHAMBERLIN 



recognize the warpings incidental to all adjustments, the recent rela- 

 tions of the continents to the seas conform to one type. The 

 10,000,000 square miles of continental margin, now submerged, is 

 distributed around the borders of all the continents with a. fair degree 

 of equability. May we not, therefore, agree that in the world-wide 

 phases of diastrophic movements, the basins have been additionally 

 depressed and the continents repeatedly rejuvenated. 



It is important that we should agree, or agree to disagree, on one 

 further point. Have diastrophic movements been in progress con- 

 stantly, or at intervals only, with quiescent periods between ? Are 

 they perpetual or periodic 7 The latter view prevails, I think, among 

 American geologists. This view has acquired especial claims since 

 base-leveling has come to play so large a part in our science, for it is 

 clear that the doctrine of base-leveling is specifically inconsistent 

 with the doctrine of perpetual deformation, for the very conditions 

 prerequisite to the accomplishment of base-leveling involve a high 

 degree of stability through a long period. The great base-levelings, 

 and the great sea-transgressions, which I think are little more than 

 alternative expressions for the same thing, have, as their fundamental 

 assumption, a suflticient stability of the surface to permit base-leveling 

 to accomplish its ends. Shall we not therefore agree that there has 

 been periodicity in the world-warping deformations ? Let this not 

 be held with such exclusiveness that we fail to recognize duly the 

 effects of the adjustment of minor stresses, at other times. These 

 may be preliminary or after-effects of the larger movements, or they 

 may be due to local stresses more or less independent of the general 

 body-stresses. These quite certainly have been present, and have 

 produced intercurrent departures from the strict tenor of the great 

 systematic movements. 



If there is need for additional argument on periodicity, it may be 

 found in theoretical considerations, but these we have tried to avoid 

 in the main. Whatever we may regard as the fundamental agencies 

 that give rise to those stresses in the earth which are precedent to 

 deformations, we may easily all agree that the earth opposes some 

 resistance to deformation. There is certainly some rigidity in the 

 body of the earth. According to the fundamental laws of rigidity, 

 the deforming stresses must reach a certain magnitude before a 



