GREWINGK GLACIER IOI 



plain inside the crescent. It is therefore probable that the 

 advance occurred only a few decades ago. 



Between 1880 and 1895 the ice retreated through a 

 space estimated by Dall at 250 feet. Between 1895 and 

 1899 the portion of the front adjacent to the south wall of 

 the valley retreated 350 feet. It happened that all of the 

 observations were made in the same month, so that the re- 

 corded changes were independent of seasonal fluctuations. 



Figure 54, representing the south wall of the valley at 

 the front of the glacier, shows the position of the ice on 

 July 21, 1899. The gravel plain and the inner push-mo- 

 raine occupy the foreground. At the extreme right a low 

 boss of rock juts from the valley wall into the gravel 

 plain, and just to the left of it is a large boulder resting on 

 a drift terrace. On July 29, 1895, Dall found barely space 

 to pass between the glacier and this boulder. 



The same view shows the barren zone of the valley 

 side and the lower limit of the forest, and the correspond- 

 ing features for the north side of the glacier are seen 

 at the left in the general view of the glacier, figure 53. 

 At the south the line of forest was about 200 feet above 

 the edge (1899) and descended westward to the gravel 

 plain in 800 feet. For some distance below the line scat- 

 tering young spruces and other bushes were seen, and 

 even within the tract uncovered since 1895 a few alders 

 had started. Nevertheless, the line of forest was clearly 

 defined, being the lower limit of mature trees, dead trees, 

 and accumulated humus. Though the line was unques- 

 tionably caused by an advance of the ice, it was not 

 marked by heaps of overturned trees, as at the La Pe- 

 rouse and Columbia glaciers. 



From these various phenomena a number of inferences 

 may be drawn: (i) For several centuries the age of the 

 forest, including its dead trees the glacier has not ex- 

 tended beyond the lower limit of the forest; that is, it 



