184 ALASKA GLACIERS 



low terraces observed in Prince William Sound are pos- 

 sibly of the same order. It is, furthermore, probable that 

 the pre-Pleistocene dissection of each area was continued 

 in association with a comparatively low base-level. In 

 view of the large number of common elements, the whole 

 region, with the exception of the high mountain district, 

 may be provisionally regarded as a unit in its later geo- 

 logic history. The uplifted peneplains do not all stand at 

 the same height, and there are important differences of 

 altitude within individual plateaus. These local differ- 

 ences suffice to show that not all changes can be ascribed 

 to the sea, and make it probable that the plateaus were 

 created by changes originating within the earth's crust. 

 The low peneplains also show minor discordances, and 

 while these also must be ascribed to crustal movement, 

 the fact that they are of moderate amount is, on the 

 whole, indicative of general crustal stability. It is a note- 

 worthy, and probably significant, fact that the oceanic 

 base-level of the region, after resting for a long time at 

 the height indicated by these low peneplains, dropped 

 below them at the time of the excavation of the fiords 

 and then returned to approximately the same position. If 

 this oscillation was an oscillation of the land, it was of the 

 broad or epeirogenic type, and the association of wide 

 extent with approximate uniformity of position after the 

 completion of the cycle is most remarkable. It would 

 seem probable that so great a general movement of the 

 earth's crust would afford opportunity for the relief of 

 local strains, and thus be accompanied by important 

 differential movements. On the other hand, sensible uni- 

 formity for any region of the magnitude here considered 

 would theoretically be a characteristic of an oscillation 

 of the sea. The local evidence, therefore, seems to me 

 more favorable to the hypothesis that the sea was low 

 during the fluvial and glacial erosion of the fiords and has 



