THE PERMIAN PERIOD. 657 



tion is not, however, out of harmony with what is known of other great defor- 

 mative movements, for in these, as a rule, the more intense foldings seem to 

 have been concentrated along restricted tracts. 



Some of the dynamic conceptions involved in such a general deformation 

 have been previously discussed (Chapter IX, Vol. I, and Chapter II, Vol. II). 

 In special application here, it may be noted that during the Subcarboniferous 

 and Carboniferous periods, in eastern America at least, a stage of approximate 

 base-level seems to have been developed over some considerable portion of the 

 territory, as shown by the configuration of the surface upon which the deposits 

 of these periods encroached, and there is reason to believe that this condition 

 was a rather general one. So far as can be judged from available evidence, 

 this conception may be extended to all of the continents; indeed, this concep- 

 tion is almost necessarily involved in the wide transgression of the seas of these 

 periods. This conception involves almost necessarily, as its essential prerequi- 

 site, the further conception of a protracted period of relative quiescence, for 

 in such a period only could base-leveling be accomplished. It is presumed 

 that during this period of quiescence, the energies that were to actuate the sub- 

 sequent deformation were accumulating stresses preparatory to actual move- 

 ment, for, in so far as loss of heat was one of the agencies, such loss must have 

 been in progress; in so far as the internal transfer of heat was concerned, it also 

 should have been in progress, and in so far as molecular changes were involved, 

 they may be supposed also to have been going forward, or to have been acquir- 

 ing the conditions prerequisite for action. It is, therefore, conceived that dur- 

 ing 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 resist- 

 ance after a protracted 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 quies- 

 cence. Considerations that have been previously presented make it appear 

 probable that a large portion of the body of the earth was involved in the defor- 

 mative movement, for, among other reasons, the portion of the crust which 

 was folded had very feeble powers of resistance and cannot reasonably be sup- 

 posed to have, of itself, accumulated 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 ultimate union in a common movement. 



The essence of the movement may be assumed, with much confidence, to 

 have been a shrinkage of the earth, preferably a general and deep-seated shrink- 

 age, rather than a purely superficial one. The shrinkage in the sectors beneath 

 the ocean basins is presumed to have been slightly greater than that in the con- 

 tinental sectors, because of the superior specific gravity the sub-oceanic sectors 

 are assumed to have acquired from their ancestral history, and because of their 

 loading by the ocean, and by the sediments brought down from the land during 

 the previous periods. At the same time, the removal of the sedimentary mate- 



