234 THE JOURNAL OF GEOLOGY. " 



When the glacier meets the sea the ice is cut away at the 

 water-level, and blocks fall from above, leaving perpendicular 

 cliffs of clear ice. At Icy cape there is a bold headland of this 

 nature from which bergs are continually falling with a thunderous 

 roar that may be heard fully twenty miles away. On the crest 

 of the cliffs of clear blue ice there is a dark band formed by the 

 edge of the sheet of debris covering the glacier, and showing that 

 the moraine which blackens its surface along its outer margin is 

 entirely superficial. At Sitkagi bluffs the glacier is again washed 

 by the sea but the base of the ice is there just above the water- 

 level and recession is slow. The bluffs are heavily covered with 

 stones and dirt, and icebergs do not form. 



At the heads of the gorges in the margin of the glacier lead- 

 ing to the mouths of tunnels, the dirt -covered ice forms bold 

 cliffs which are most precipitous at the heads of the reentrant 

 angles. The eastern margin of the ice sheet, facing Yakutat bay, 

 is low and covered to a large extent with water -worn debris. 

 The ridges on the glacier formed by moraines are there at right 

 angles to the margin of the ice and are bare of vegetation. The 

 reason for the exceptionally low slope of the eastern margin of 

 the ice sheet seems to be that the current in the ice is there 

 eastward and the glacier is melting back without leaving a stag- 

 nant border. 



Marginal lakes. — The water bodies here referred to are called 

 " marginal lakes" for the reason that they are peculiar to the 

 margins of glaciers. Where rocks border an ice field or project 

 through it they become heated, especially on southern expos- 

 ures, and, radiating heat to the adjacent ice, cause it to melt. A 

 depression is thus formed along the margin of the ice, which be- 

 comes a line of drainage. Water flowing through such a chan- 

 nel accelerates the melting of the ice, at least until a heavy coating 

 of debris has accumulated. When a steep mountain spur projects 

 into an ice field the lines of drainage on each side converge and 

 frequently unite at its extremity, forming a lake, from which the 

 water usually escapes through a tunnel in the ice. Typical 

 instances of lakes of this character occur at Terrace point, at the 



