EVIDENCES OF RECENT FAULTING - ,< 51 



tion was such as to make.it possible to interpret the fracturing there as 

 the result of sapping along nearly vertical strata above a stream-cut cliff. 

 On Gannett nunatak, and in the other places, the situation of the faults 

 precludes the possibility of this interpretation, and it is doubtful if even 

 in the case mentioned the interpretation of sapping is the correct one. 



Such shattering near a cliff edge would not only cause avalanches dur- 

 ing the earthquake, but also prepare the way for future avalanches by 

 opening passageways into the rock. Thus in this respect faulting is an 

 important agent of denudation in favorable localities. 



OTHER INSTANCES OF RECENT FAULTING 



Similar faults were observed in a number of other places, but nowhere 

 in such numbers as on Gannett nunatak. Eecent faults were discovered on 

 the southern slope of mount Tebenkof (strike, north 45 degrees west and 

 north 65 degrees west, true north) and on the ridge south of point 

 Latouche (north 85 degrees east, true north), where, at an elevation of 

 about 1,900 feet, there are a number of faults in a moraine. Several of 

 these have a throAv of 3 feet. That the latter can not be due to landslip 

 action is proved by the fact that they cross a valley and extend up the 

 slope of a hill near its middle and several hundred yards away from the 

 nearest steep slope. Eecent faults were also observed by Mr Butler and 

 the junior author on a nunatak on the west side of Lucia glacier and on 

 the west spur at the south of Floral pass. 



Thus in several widely scattered localities minor faulting was observed, 

 and in a number of places not visited there appeared to be such faults on 

 the mountain slopes; but no case of a single major fault-scarp was ob- 

 served. The significance of these facts is considered in a later section. 



Evidences of Older Changes of Level 

 evidence of older fault lines 



Largely on physiographic evidence, Russell assigned to faulting a nota- 

 ble part in the production of the topography of the Yakutat Bay region, 

 and of the mountains up to and including mount Saint Elias, which he 

 describes as a fault block recently uplifted. So far as they go, the 

 tendency of our observations is toward the verification of RusselFs gen- 

 eralizations, in so far as the Yakutat Bay region is concerned. The 

 straight mountain front from Yakutat bay southeastward, with its trun- 

 cated mountain spurs (plate 22, figure 1), has the form of a fault-block 

 mountain front, though we have no facts to prove that it is not an ancient 

 sea cliff, formed before the deposit of the gravels of the Yakutat foreland. 



