296 GLACIAL GRAVELS OF MAINE. 



ENGLACIAL STREAMS. 



Recent observations of the Alaskan glaciers warrant the belief that 

 englacial streams are sometimes of geological importance, or perhaps it 

 might be better stated that the englacial portions of streams that are sub- 

 glacial or superglacial for the rest of their course have helped in the 

 development of the glacial sediments.^ 



It is evident that any conditions that prevent the formation of crevasses 

 in the lower part of the ice will hinder, if not prevent, the formation of sub- 

 glacial tunnels, at least as conduits for waters of surface melting. Where 

 crevasses re;ach only part of the distance down to the bottom of the ice, 

 the superficial water would often form an englacial channel along the bot- 

 tom of the crevasses. The collapse or blocking of a subglacial tunnel 

 would cause the water to rise and escape superglacially, or in case of cre- 

 vasses it would form a new channel either at the bottom of the ice or above 

 it englacially. In a sin-inking glacier the melting of the ice forming the 

 roof of an englacial tunnel would leave it as a superglacial stream. The 

 stream reported by Russell as rising on the Lucia glacier where it flows 

 past a nunatak woiild appear to have formerly had an englacial channel at 

 this place, now become superficial by melting. The situation suggests 

 that the course of glacial rivers in such relations may have been deter- 

 mined by the fact that the ice of the deep valley at the sides of the nunatak 

 was so compressed laterally as it pai-ted and flowed around the hill that the 

 basal ice was little broken by crevasses. Crevasses would naturally form' 

 over the top or higher flanks of the hill, but would not reach below some 

 point on the hillside. These shallow crevasses were utilized by the stream 

 as part of its channel. 



Englacial streams and channels of the ice-sheet may have performed 

 two different offices. 



First, they may have amassed glacial sediments directly from the ice. 

 Whether we consider them of importance as gatherers of glacial sediments 

 will largely depend on our conception of the distribution of the ddbris in 

 the ice. The only way such streams could directly collect glacial sediments 

 would be by melting the ice around the ddbris and transporting it. The 



I Prof. I. C. Eussell, Nat. Geog. Mag., vol. 3, pp. 106, 107, May, 1891. Am. Jour. Sci., 3d series, 

 vol. 43, p. 180, Marcb, 1892. Also Prof. G. F. Wright, Ice Age in North America, p. 63, 1889. 



