MALASPINA GLACIER. 243 



they form, but the greater and practically the entire accumulation 

 is more or less rounded and waterworn. Cross stratification 

 characterizes the deposits throughout, and on the surface of 

 many of the cones, and probably in their interior, also, there are 

 large quantities of broken tree trunks and branches. The coarse 

 deposits first laid down on a growing alluvial cone are buried 

 beneath later deposits of finer material in such a way that a 

 somewhat regular stratification may result. A deep section of 

 one of these deposits should show a gradual change from fine 

 material at the top to coarse stones and subangular bowlders at 

 the bottom. Their outer borders are of fine sand and mud, and 

 when the distance of the ocean is sufficient, the streams flowing 

 from them deposit large quantities of silt on their flood plains. 

 The very finest of the glacial mud is delivered to the ocean and 

 discolors its water for many miles from land. 



The formation of alluvial cones about the border of a stag- 

 nant ice sheet, and the deposition of ridges of gravel within it, have 

 an intimate connection and are in fact but phases of a single pro- 

 cess. The growth of an alluvial cone tends to obstruct the 

 mouth of the tunnel through which its feeding stream discharges; 

 this causes the stream to deposit within the tunnel ; this, again, 

 raises the stream and allows it to build its alluvial cone still 

 higher. In the case of Malaspina glacier where this process has 

 been observed, the ice sheet is stagnant, at least on its border, 

 and is retreating. The ground on which it rests is low, but is 

 thought to be slightly higher on the southern margin of the 

 glacier than under its central portion. The best development of 

 alluvial cones and osars would be expected in a stagnant ice 

 sheet resting on a gently inclined surface, with high lands on the 

 upper border from which abundant debris could be derived. 

 These ideal conditions are nearly reached in the example 

 described. 



Glacial and ocean records. — Much has been written concern- 

 ing the character of the deposits made by glaciers when they 

 meet the ocean, but so far as can be judged from the condi- 

 tions observed about the borders of Malaspina ice sheet, the sea 



