1870.] BROWN—PHYSICS OF ARCTIC ICE. 681 
MOS MEHTAT STs 6/5, Set) a4 se s/s) Uys in about N. lat. 70 52 
DSI IONMMC RIG Med agey ia) exe) aay 8 aint oy da i 70 56 
12. Great Kangerdlursoak........ 5h 71 25 
Ue Wpermivale Vices cess 52 Faye 45 72 57+ 
We have now sketched the ice-field with the glacier and the iceberg. 
Are there no other defluents of the “inland ice”? This leads us to 
speak of :— 
4. The Subglacial Stream.— What is under the inland ice is, I 
fear, a question we shall never be able to answer. No doubt the 
country is undulating; for, I believe, this immense glaciation over- 
spread the country after the close of the Tertiary period, perhaps 
about the same period when Scotland lay under the ice cap. Conti- 
nuously grinding over these rocks, a creamy mud must be formed, 
which mud must now be of considerable thickness if not swept into 
hollows or washed out from beneath the ice. In the Alps the 
glacier is said to wear for itself a muddy bed, which Agassiz? calls 
la couche de boue or la boue glaciare, and other authors la moraine 
profonde (fig. 1, 6); so that, I think, there can be little doubt that 
the Greenland inland ice has triturated down a similar clayey bed. 
However, another instrument in the arrangement and, if I may 
use the term, “utilization” of this mud, this moraine profonde, 
comes into play. Rink’ has calculated the yearly amount of pre- 
cipitation 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 con- 
siders 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 subglacial rivers. These subglacial rivers are 
familiar in all alpine countries, and in Greenland pour out from be- 
neath 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 out- 
fall 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 connexion 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 ac- 
counts 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 incon- 
siderable portion of the glacier, whose thickness exceeds 2000 feet. 
As in the alpine glaciers, these subglacial rivers are thickly loaded 
1 Rink: Om den geographiske beskaffenhir af den Danske Handels districter, 
i Nord Grénland (Afskrf. af Vidensk. Selskab. Skr. 5 -3 3), e¢ lid. cit. 
2 Etudes sur les Glaciers et Systéme Glaciaire, p. 574, 
3 Naturhistorisk Tidsskrift, 3rd series, vol. i. part 2 (1862), and Proc, Roy. 
Geogr. Soc. vii. 76. 
3D 2 
