68 THE ICE AGE IN SORTH AMERICA. 



My estimates concerning the amount of sediment carried 

 out by subglaeial streams are as follows : The amount of sedi- 

 ment contained in each United States gallon t^23i cubic inches) 

 of water collected from the subglaeial streams is. as deter- 

 mined by the analysis of the late Professor H. C. Foote, of 

 Cleveland, 708'48 grains. Estimating the total area occupied 

 by the glacial amphitheatre to be 1,200 square miles, and the 

 annual precipitation the same as that at Sitka iwhich is not 

 far from ninety-six inches', the total amount of water which 

 must in some form annually pass into the inlet from this area 

 is 267,632.640,000 cubic feet. Of this amount I estimate 

 that 77,088,000,000 cubic feet passes out as ice. or, reducing 

 this to water, about 67,000,000,000 cubic feet of liquid water. 

 i^This part of the calculation is based on the fact approximate- 

 ly ascertained that a section of ice one mile wide and 1.000 

 feet deep is moving into the inlet at a rate of 40 feet per 

 day.) Subtracting the ice from the total amount, and esti- 

 mating that evaporation would probably diminish the amount 

 one eighth, the total amount of water which must issue in 

 all the subglaeial streams from this glacier is 175,000,000,000 

 cubic feet. Estimating the specific gravity of the sediment 

 (which is chiefly some compound of alumina and silica) at 

 two and a half, we have, as the total amount of sediment 

 transported thus, 33.274,804 cubic yards. This equals not far 

 from one third of an inch per year eroded from the total 

 area (1,200 square miles') occupied by the glacier. This 

 would furnish one inch of sediment per year to be spread by 

 this single glacier over the bottom of Glacier Bay. This 

 confirms the statements concerning the recent recession of 

 the glacier from the lower poition of the bay, since otherwise 

 it would now be full of sediment. 



Besides the Muir Glacier several others of large size, 

 such as the Grand Pacific and Hugh Miller Glaciers, descend 

 from the flanks of Mts. Crillon and Fairweather into Reid 

 Inlet, w hich projects several miles to the northwest from 

 Glacier Bay. These do not differ materially in appearance 

 and behavior from the Muir Glacier. 



