FOUNTAINS AND STREAMS 243 



developed, issuing from cavelike openings on the 

 melting margin and growing longer as the ice 

 withdrew ; while for many a century the tributa- 

 ries and upper portions of the trunks remained 

 covered. In the fullness of time these also were 

 set free in the sunshine, to take their places in 

 the newborn landscapes ; each tributary with its 

 smaller branches being gradually developed like 

 the main trunks, as the climatic changes went on. 

 At first all of them were muddy with glacial 

 detritus, and they became clear only after the 

 glaciers they drained had receded beyond lake 

 basins in which the sediments were dropped. 



This early history is clearly explained by the 

 present rivers of southeastern Alaska. Of those 

 draining glaciers that discharge into arms of the 

 sea, only the rills on the surface of the ice, and 

 upboiling, eddying, turbid currents in the tide 

 water in front of the terminal ice wall, are visible. 

 Where glaciers, in the first stage of decadence, 

 have receded from the shore, short sections of 

 the trunks of the rivers that are to take their 

 places may be seen rushing out from caverns 

 and tunnels in the melting front, — rough, roar- 

 ing, detritus-laden torrents, foaming and tum- 

 bling over outspread terminal moraines to the 

 sea, perhaps without a single bush or flower to 

 brighten their raw, shifting banks. Again, in 

 some of the warmer canons and valleys from 

 which the trunk glaciers have been melted, the 



