GLACIERS OF ALASKA. 355 



3. All the larger glaciers formed extensive overwasli aprons or sheets 

 of water-rolled material, which are coarser in composition at the principal 

 terminal moraines and become finer as we go down the valleys below them. 

 This glacial gravel was deposited in diminishing quantities as we go 

 upward from the outer terminal moraines. The retreatal terminal moraines 

 extend higher up the valleys than the water-rolled matter, and often we 

 find above the last gravel deposit a number of retreatal moraines scattered 

 over a space of a mile or two. Almost every valley in the mountains 

 attests that the small glaciers that marked the final disappearance of the 

 ice formed but little glacial sediment, and what there is shows only a lim- 

 ited amount of waterwear. 



4. The glacial gravel is deposited in rather level or even jjlains or 

 terraces, sometimes rising one above another as we go back into the moun- 

 tains. No ordinary kames or osars are found, though the low ridges 

 transverse to the course of the glacier above noted are in some degree a 

 correlative deposit to the retreatal moraines and "kames" observed by 

 Wright near the Muir glacier. They are an eighth of a mile broad, and 

 the interpretation is doubtful. They are well developed in a small A'alley 

 3 miles north of Twin Lakes in the Arkansas Valley. In several places, 

 such, for instance, as the valley of the Arkansas 12 miles south of Lead- 

 ville, on the east side of the river, there is a jumble of heaps and ridges of 

 glacial gravel, but this is due to unequal erosion of a once continuous sheet. ' 



The sheets of glacial gravel of the Rocky Mountain glaciers are rather 

 horizontall}^ stratified and in their surface features resemble the broad osars 

 or osar terraces of Maine. They are the equivalents of the deposits I have 

 termed "frontal deltas" in Maine. But whereas in the mountains the finer 

 clay and sand was at once swept away by the rapid streams, except locally 

 in glacial lakes, in Maine the slopes were so gentle that they form broad 

 sheets of silts and clays widely covering the A^alleys all the way to the sea- 

 shore of that time. 



GLACIERS OF ALASKA. 



The origin of frontal or overwasli aprons of glacial gravel, also of 

 kames such as are formed b}" valley glaciers, is illustrated by the Mount 

 St. Elias glaciers described by Prof. Israel C. Russell.^ The MalasjDina 



■ Kat. Geog. Mag., vol. 3, pp. 53-204; also Am. Jour. Scl., 3fl series, vol. 43, pp. 169-182, Marcli, 1892. 



