GLACIAL EROSION IN ALASKA 103 



discordance in the other directions mentioned above, calls for ex- 

 planation. 



The partial submergence of a region traversed by a series of val- 

 leys with the characteristics just stated, would produce results which 

 can be readily and accurately predicted. The line up to which the 

 new sea level reached would be rendered irregular for two reasons. 

 In the first place, the overlapping spurs would introduce a winding 

 coast line in the fiords, with capes on one side opposite reentrants on 

 the other. In the second place, since the tributary valleys joined the 

 main valleys at grade, the sea water would enter their mouths and thus 

 transform their lower portions to bays. 



Examining the actual conditions along the Inside Passage to 

 Alaska, we find very wide departures from this postulated result of a 

 drowning of normal land valleys. Many of the passages are in the 

 form of long straight ' Peaches ' and ' Canals,' up and down which one 

 can look for miles without obstruction to the view. In other cases the 

 ' Reaches/ though not perfectly straight, have alternating projections 

 and reentrants (Fig. 1). These, however, depart from typical over- 

 lapping spurs in two important respects. In the first place, they are 

 much less pronounced. In the second place, instead of having a uni- 

 form slope from the crest to the tip of the spurs, they have a moderate 

 slope above, like that of ordinary valley spurs, but terminate on the 

 water side in a steep and even precipitous slope. They have the ap- 

 pearance, therefore, of being truncated valley spurs; and a view 

 through such a channel often shows a succession of these partial 

 spurs with the truncated faces in alignment. The general appearance 

 of these aligned spurs suggests that some powerful rasping agent has 

 moved through the fiord and truncated the overlapping spurs back to 

 a fairly uniform distance. 



The fiords of the Inside Passage furnish all gradations from typical 

 overlapping spurs to aligned spurs, and to straight, smoothed i Canals ' 

 from which all semblance of spurs has been erased. In the latter case 

 the valley walls themselves often possess a double slope, steep and 

 even precipitous below, more gentle above. The steepened lower slope 

 has the appearance of having been incised in a valley whose remnant 

 is represented by the upper more gentle slope. 



In those ' Peaches ' which are long and straight, and in those with 

 aligned spurs, the tributary valleys enter the main valley at very differ- 

 ent levels. Some, especially the larger, enter below the level of the 

 sea, and in these cases there are bays in their mouths (Fig. 2) ; many 

 others have their mouths high above the fiord level (Figs. 3, 4 and 5). 

 Although there is no uniform height at which these side valleys enter 

 the main trough, in general it is true that, the smaller the tributary 

 valley, the higher its mouth lies above the main valley bottom. These 

 are called hanging valleys because their mouths hang above the bottom 



