DEFORMATION AND GRADATION. 303 



movement. It is, therefore, conceived that during the quiescent stage 

 stresses were progressively accumulating in the body of the earth, but that 

 they only reached an intensity superior to the earth's resistance after a pro- 

 tracted period. When at length they surpassed all resistances, deformation 

 went slowly forward until the stresses were, in the main, relieved, and the 

 earth was thus prepared to relapse into another stage of relative quiescence. 

 Considerations that have been previously presented make it appear probable 

 that a large portion of the body of the earth was involved in the deformative 

 movement, for the portion of the crust which was folded had very feeble powers 

 of resistance and can not reasonably be supposed to have, of itself, accumu- 

 lated stresses of the magnitude implied by the actual deformation. The 

 phenomena seem to point to a high state of rigidity in the great body of the 

 earth, and to the accumulation of very widely distributed stresses which were 

 feeble at every point, and which only acquired effective strength by their ulti- 

 mate union in a common movement." 



While this grand cycle consisted of two great phases, one of active deforma- 

 tion and the other of gradation or base-leveling, it is clear that the two proc- 

 esses were contemporaneous. The phases and hence the cycle itself were due 

 not to the absence of one process, but to the overwhelming emphasis of the 

 other. Erosion and deposit went on throughout the period of deformation, 

 but they could have reached a maximiun only after it had been completed. 

 Minor deformative changes doubtless occurred throughout the period of 

 relative quiescence marked by the slow but steady decrease of gradation from 

 a maximum to a minimum. During this phase, various causes combined to 

 produce cimiulative stresses which initiated a new major deformation and 

 carried it to a maximum. The magnitude of deformation not only varied 

 greatly throughout the cycle, but it was obviously much greater in some regions 

 than in others. Moreover, at the time of active deformation there must have 

 existed a complementary relation between regions of great elevation and less 

 elevation. Clearly all of these movements belonged to one great cycle, but 

 the latter is best seen in the areas of maximimi displacement. Within this 

 grand cycle exist minor cycles of nearly every degree, down to the initial 

 development of gullies and ravines at the present time. 



Every cycle initiated by deformation is essentially an erosion cycle. There 

 are, however, many degrees of deformation, and the corresponding erosion 

 cycles differ in intensity, extent, and duration. From the standpoint of 

 succession, at least, it is hslpful to distinguish the great cycles of deformation 

 and gradation from the minor ones of varying degree. Consequently, the 

 term "deformation cycle" is restricted to the great body deformations of 

 more or less world-wide extent, and to the grand erosion period that follows. 

 Within this grand cycle are many lesser cycles, characterizing shorter periods 

 or affecting particular regions or restricted areas, often no larger than a small 

 river system or a part of it. Such are here regarded as cycles of erosion. To 

 the geologist and geographer such a distinction may seem worthless, but to 

 the ecologist it distinguishes the primary earth changes with their major 

 sequences of climate and vegetation, from the host of secondary ones, all of 

 lesser importance in themselves as well as in their sequences. This distinc- 

 tion seems, moreover, to be in general accord with the views of Chamberlin 

 and Salisbiuy. They seem nowhere to use the term cycle of erosion in the 

 discussion of deformation and its topographic sequences (1906: 1 : 542; 2: 656; 



