INTERPRETATION OF OBSERVATIONS 61 



a part of the evidence on which a fault line is inferred with some doubt 

 along the axes of these islands. 



FAULT ALONG EAST SHORE OF YAKUTAT BAY 



Much clearer evidence of a fault line exists along the mountainous 

 eastern shore of Yakutat bay (see unlettered fault line B, plate 23). 

 Here the mountain front is straight, steep, and has spurs truncated along 

 a straight line. The mountain face is scarred by numerous avalanches, 

 and the shores at its base were washed by the most destructive tidal wave 

 recorded in the region (plate 20, figure 1). For much more than half its 

 length this shore shows no elevated strands; but they begin where the 

 coast bends away from the straight line on both the north and south end ; 

 and near the middle, where the mountain slopes come down close to the 

 sea, there is an upraised ancient beach and, parallel to it, an uplift belong- 

 ing to the 1899 series (see figure 2). 



We are able to suggest no other explanation for the phenomena re- 

 corded here than that of a fault close to the mountain base, lifting the 

 hard rock of the mountains, but not raising the gravel forelands which 

 skirt most of this straight coast. In this connection it is notable that be- 

 hind the broadest part of the narrow foreland, at Logan beach, there is 

 a valley between the foreland and the mountains, whose formation by 

 earlier faulting is easy to understand, but difficult of explanation in any 

 other way. That the earthquake shock was violent here is proved by the 

 fact that a gold miner's log cabin on the gravel bluff above Logan beach 

 was partially demolished, unroofed, and thrown part way off of its founda- 

 tions during the earthquake of 1899. 



We are not absolutely certain whether to correlate this fault with the 

 one inferred farther southeast along the mountain front (plate 23, 

 fault A), which it intersects at a low angle, assuming the two to be con- 

 nected by a slight bend, or whether to consider it a separate and distinct 

 fault. The later interpretation is placed on the map, but we have no evi- 

 dence to prove this interpretation as opposed to that of a single contin- 

 uous, slightly curved fault line. It is a notable fact that this fault line, 

 extended, strikes the western side of the head of Yakutat bay exactly at 

 the point where the great uplift south of Turner glacier dies out. 



FAULTING ALONG DISENCHANTMENT BAY 



The great uplift (reaching over 47 feet) on the west shore of Disen- 

 chantment bay; the lesser, but still great (18 to 19 feet), uplift on 

 Haenke island and the shore of the peninsula north of it; and the mod- 

 erate uplift (7 to 9 feet) along most of the east shore of Disenchantment 



VII— Bull. Geol. Soc. Am., Vol. 17. 1905 



