60 TARR AND MARTIN CHANGES OF LEVEL IN YAKUTAT REGION 



these differential movements is not certain in all cases, though some con- 

 clusions regarding them seem clear and well founded. 



MOUNTAIN-FRONT FAULT 



That there is a zone of narrow width, just outside the mountain base, 

 where uplift is replaced by either depression or no change, is clearly 

 shown at four points. This suggests the presence of a fault line near the 

 mountain base. If such a line is projected (see fault line A, plate 23) 

 it passes through three of the areas where uplift is replaced by depression 

 or no change, but would need to be bent slightly to reach the fourth at the 

 head of Yakutat bay on the west side. From this evidence a fault line is 

 inferred along the face of the mountain from the head of Eussell fiord 

 to Knight island. 



Additional reason for suspecting an older fault here is found in the 

 topography already described — a straight mountain front with truncated 

 spurs reaching out to nearly the same line (plate 22, figure 1). Along 

 this line, northeast of Knight island, there is also an unusual develop- 

 ment of avalanches. Moreover, the amount of uplift along it varies 

 greatly, as it naturally would along a fault with the downthrow side 

 dragged upward, and with the fault line not a single break but a complex 

 of parallel fractures, as seems to have been the case in this region, where 

 the change across the fault line is not an abrupt scarp, but occupies a zone 

 of some width. The statement of Ensign Miller that trees are destroyed 

 on the east and west side of Miller lake is interesting, since this is exactly 

 where we place our fault line on entirely independent evidence. 



Harmonious with the interpretation placed on the facts in this 

 region is the appearance of the four small islands east of Knight island, 

 exactly where the inferred fault is believed to pass, and with their long 

 axes parallel to the fault line. We do not place this fault line outside the 

 zone of uplift because it is believed that some of the upraised coast near 

 and on Knight island is due to updrag on the downthrow side. 



POSSIBLE MINOR FAULT SOUTHWEST OF KNIGHT ISLAND 



There is the possibility of a second fault of minor character along the 

 islands between Knight island and Yakutat (see fault line, plate 23). 

 The evidence of this is not convincing, and this fault is proposed solely 

 on the basis of the fact that there is a rather remarkable linear arrange- 

 ment of uplifted and depressed areas in the midst of a region which, in 

 general, shows no sign of change in level. The fact that earlier changes 

 of level are recorded in these same places by older uplifted beaches, and 

 that similar shorelines were not discovered elsewhere in the foreland, is 



