60 AN OUTLINE OF THE 



their surroundings that indicate intrusion at great depths 

 beneath the surface of their time. Now it is a law, well 

 demonstrated in the science of land sculpture, that an even 

 upland of large extent, like that of the New England pla- 

 teau, in which there is at present no sympathy between 

 rock structure and surface form, can be produced only in 

 the later stages of a long cycle of denudation, when the 

 region has wasted from whatever height it once possessed 

 nearly down to sea level, or base level as it is conveniently 

 called. The New England upland was therefore once, not 

 only at its margin as now, but across its whole extent, a 

 lowland of denudation standing near sea level; and its 

 present elevation must have been given to it at some sub- 

 sequent time by an unequal tilting which depressed part 

 of its former extent beneath the sea, and which raised the 

 inner portion of its area one or two thousand feet. 



The reader must guard against making too even a 

 picture of this ancient plain of denudation. It was by 

 no means a dead-level plain, but a rolling surface of mod- 

 erate relief, an almost plain surface, for which I have 

 coined the term peneplain. During the long cycle of 

 denudation, the region was not entirely worn down to sea 

 level, but it was greatly reduced from the height that it 

 once possessed, and only low hills remained to represent 

 most of its ancient mountains. At certain points, not 

 even the peneplain stage was reached. The view across 

 the New England upland nearly always includes, in one 

 direction or another, an eminence rising above the general 

 sky line ; and of such, Monadnock in southwestern New 

 Hampshire is one of the most beautiful examples. These 

 eminences, once overlooking the lowland, but now overlook- 

 ing the plateau, are residual mountains, which by reason 

 of their excessive hardness escaped the nearly complete 

 denudation that the rest of the peneplain suffered. The 

 White Mountains seem to be simply a cluster of Monad- 



