82 THE ICE AGE IN NORTH AMEBIC A. 



Helland's observations as to the amount of ice floating 

 away from the glacier in bergs amply confirm the direct cal- 

 culation. The depth of the Jakobshavn Fiord is about 

 1,200 feet, so that icebergs cf vast size can float off upon its 

 waters. The daily discharge of ice through this fiord was 

 estimated by him to be 432,000,000 cubic feet — about three 

 times the calculation I have made for the Mnir Glacier in 

 Alaska. In addition to the formation of large icebergs, the 

 discharge of ice from such a glacier as that at Jakobshavn is 

 doubtless accompanied by a continual cannonade of countless 

 smaller fragments, keeping the heavens full of thundering 

 sounds and the waters full of commotion. From this it fol- 

 lows that the movement of the great glaciers must be rapid, 

 to account for the enormous numbers of first-class icebergs 

 which are encountered in the vicinity, and for the numerous 

 and immense ice-floes composed of smaller fragments. 



While the attention is fixed on the movement of the gla- 

 ciers, we should not fail to note the uniform presence of 

 subglacial streams of water emerging from their fronts. 

 Such streams are usually in proportion to the size of the gla- 

 cier, and, as already remarked, are most powerful agencies in 

 the transportation of earthy material. The amount of sedi- 

 ment thus brought out by a single subglacial stream on the 

 west coast of Greenland is estimated to be from 15,000 to 

 20,000 tons daily ; and the amount of water discharged in 

 the stream is far larger than that which passes off as ice. 



The existence of such subglacial streams reveals much 

 concerning the condition of the glaciers themselves. The 

 question at once arises. Whence does the water come ? The 

 answer is found in the facts already mentioned by Norden- 

 skiold concerning the superficial streams of water uniformly 

 encountered on penetrating the glaciated interior of Green- 

 land. Doubtless, also, much water arises from the melting 

 of the lower strata of ice through the heat produced by the 

 friction attendant upon the motion. 



Mr. Whymper's descriptions add vividness to our knowl- 

 edge of the Greenland Glacier in the latitude of Disco : 





