INTERPRETATION OF OBSERVATIONS 63 



without success. Opposed to folding are four significant facts which seem 

 to eliminate it as an hypothesis. In the first place, the lines of deforma- 

 tion extend in too many directions. In the second place, the zones of 

 gradation between areas of different degrees of deformation are exceed- 

 ingly narrow, while the intervening areas of uplift are very broad. In 

 the third place, the minor faulting proves dislocation in parts of the 

 region. Finally, faulting is proved by the series of earthquakes and their 

 destructive avalanches and water waves. 



NATURE OF THE DEFORMATION 



Briefly summarizing the inferences which the facts seem to warrant, we 

 conclude that in 1899 there was a renewal of mountain growth, uplifting 

 that part of the mountain front bordering the Yakutat bay inlet to differ- 

 ent amounts — 7 to 10 feet on the southeast side of the bay and 40 to 47 

 feet on the northwest side. This uplift occurred all within a little over two 

 weeks and mainly on a single day (September 10). It was complicated 

 by movements along secondary fault lines, which produced at least three 

 (and perhaps more) distinct major blocks, as follows: (1) The area be- 

 tween fault lines A, B, C, and E (plate 23), including all the peninsula 

 and a part of the mountains east of the south arm of Russell fiord to an 

 unknown distance toward the southeast ; ( 2 ) a block west of fault line E 

 (plate 23), extending westward an unknown distance from the west 

 shore of Disenchantment bay; (3) a block extending northeastward for 

 an unknown distance from the northeast shore of the northwest arm of 

 Russell fiord. The first and largest of these blocks, that including the 

 peninsula, is apparently tilted upward toward the southwest. 



Accompanying this faulting was a minor fracturing apparently due to 

 local adjustments in the tilted blocks. Doubtless this minor fracturing 

 is much more common than our observations indicate, for it was discov- 

 ered in more than half of our expeditions into the interior when we went 

 out of the valleys away from the seacoast. 



TOPOGRAPHIC SIGNIFICANCE 



That this faulting may be part of an important process by which the 

 main lineaments of topography in this region were developed is evident. 

 The straight mountain front, the straight mountainous eastern shore of 

 Yakutat bay, and the straight northwest arm of Russell fiord all bear evi- 

 dence of faulting during this recent period of uplift, and the evidence 

 seems to demand the presence of two fault lines along Disenchantment 

 bay. How far this process of faulting can be applied in explanation of 

 the initial outlining of the fiords is not certain from any facts we could 



