RATE OP GLACIAL FLOW. 197 



Reicl and Gushing in 1890, the ice-front had receded one-third to two- 

 thirds of a mile. 



In 1886 the height of the ice-cliffs above the water was found by Wright 

 to be 250 to 300 feet, and the rates, of forward motion of the most promi- 

 nent ice pinnacles near to the front and within a half mile back from it 

 were roughly measured by him and found to vary from 160 feet to 9 feet 

 per day, the maximum being that of a pinnacle close to the projecting 

 middle of the terminal cliffs. In 1890, however, Reid and Gushing 

 measured the rates of the glacial currents in a more accurate way by 

 observations of flags set on the surface of the glacier one-fourth to one- 

 half of a mile back from its then nearly straight and much lower front, 

 and found the maximum movement near the center to be only about 

 seven feet per day. In respect to the apparent discrepancy of these de- 

 terminations in 1886 and 1890, it is to be remarked that the ice pinnacles, 

 belonging to the most fractured and crevassed portions of the glacier, 

 probably move onward faster than its more even tracts, which can be 

 traversed and marked by flags, and that the two different years between 

 which the front was withdrawn so far may have been considerably unlike 

 in the meteorologic conditions governing the flow of the glacier. The 

 abundant observations of Helland, Steenstrup and others on the rates of 

 outflow of glaciers into the fjords and bays of the western coast of Green- 

 land show that there the glacial advance ranges frequently from 30 to 65 

 feet daily, and in at least one case is about 100 feet.* Narrow glaciers 

 in Alpine valleys move only a few feet daily ; but the broad glaciers 

 of polar regions, when they terminate in the sea, often move at their 

 ends much more rapidly, as 30 to 50 feet or more per day. 



The Muir glacier, like the Malaspina ice-sheet and other glaciers of the 

 Saint Elias region, is fast retreating. From the narrative of Vancouver's 

 exploration of this coast in 1794, and from observations by Wright, Reid, 

 and Gushing, of freshly glaciated rock surfaces far outside and also far 

 above the present glacier, it appears sure that only one to two centuries 

 ago the Muir glacier stretched some twenty miles farther than now, nearly 

 to the mouth of Glacier bay. Its advance to this maximum area had 

 perhaps occupied a considerably longer time than its retreat, but the 

 whole time of both advance and recession appear to be geologically 

 recent. In its forward movement forests became enveloped in the gravel 

 and sand discharged by streams from the glacier, and they were then 

 overridden by the ice advance, so that now on its retreat the still stand- 

 ing trees are being uncovered by the channeling of streams. 



During the summer of 1890 the rate of ablation of the frontal part of 



*H. Rink: "The Inland Ice of Greenland," Scottish Geog. Mag., vol. v, L889, pp. 18-28. Nature, 

 December 29, 1887. 



