THE SUB-GLACIAL STREAM. 39 



(fig. 1,6); so that, I think, there can be little doubt that the Green- 

 land inland ice has triturated down a similar clayey bed. However, 

 another instrument in the arrangement, and, if I may use the term, 

 ''utilisation" of this mud, this moraine profonde, comes into play. 

 Eink 1 has calculated the yearly amount of precipitation in Greenland 

 in the form of snow and rain at 12 inches, and that of the outpour 

 of ice by its glaciers at 2 inches. He considers that only a small 

 part of the remaining 10 inches is disposed of by evaporation, and 

 that the remainder must be carried to the sea in the form of sub- 

 glacial rivers. These subglacial rivers are familiar in all Alpine 

 countries, and in Greenland pour out from beneath the glacier, 

 whether it lies at the sea or in a valley, and in summer and winter. 

 He also mentions a lake adjacent to the outfall of a glacier into the 

 sea, which has an irregularly intermittent rise and fall. " Whenever 

 it rises, the glacier-river disappears ; but when it sinks, the spring- 

 bursts out afresh," — showing, as he thinks, a direct connection 

 between the two. Arguing from what has been observed in the 

 Alps, he concludes that an amount of glacier-water equivalent to 

 10 inches of precipitation on the whole surface of Greenland is not 

 an extravagant hypothesis ; and he accounts for its presence partly 

 by the transmission of terrestrial heat to the lowest layer of ice, and 

 partly by the fact that the summer heats are conveyed into the 

 body of the glacier, while the winter cold never reaches it. The 

 heat melts the surface-snow into water, which percolates the ice, 

 while the cold penetrates a very inconsiderable portion of the 

 glacier, whose thickness exceeds 2000 feet. As in the Alpine 

 glaciers, these subglacial rivers are thickly loaded with mud from 

 the grinding of the glacier on the infrajacent rocks ; in fact, from 

 the washings of the moraine prof onde. This stream flows in a torrent 

 the whole year round, and in every case which I know of (in the 

 Arctic regions) reaches the sea eventually, though, no doubt, parting 

 on the way with some small amount of its suspended mud. After 

 it reaches the sea it discolours the water for miles, finally depositing 

 on the bottom a thick coating of impalpable powder. When this 

 falls in the open sea it may be scattered over a considerable space ; 

 but when (as in most cases) it falls in narrow long fjords, it collects 

 at the bottom, shoaling up these inlets for several miles from their 

 heads, until, in the course of time, the fjord gets wholly choked up, 

 and the glacier seeks another outlet or gets choked up with bergs, 

 which slowly plough their way through the deep banks of clay, 

 until they get so consolidated together as to shut off the land alto- 



1 ' Naturbistorisk Tidsskrift,' 3rd Beries, vol. i. part '2. (1862), and 'Proc, Boy. 



1 •• Og. Sue.,' vii. 76. 



