GLACIAL MOTION. 47 



land. The Jakobshavn Glacier was about two and a half 

 miles in width and its depth very likely more than a thou- 

 sand feet, making a cross-section of more than 1,400,000 

 square yards, whereas the cross-section of the Mer de 

 Glace at Montanvert is estimated to be but 190,000 square 

 yards or only about one-seventh the above estimate for 

 the Greenland glacier. As the friction of the sides 

 would be no greater upon a large stream than upon a 

 small one, while upon the bottom it would be only in pro- 

 portion to the area, it is evident that we cannot tell be- 

 forehand how rapidly an increase in the volume of the 

 ice might augment the velocity of the glacier. 



At any rate, all reasonable grounds for distrusting the 

 accuracy of Helland's estimates seem to have been re- 

 moved by later investigations. According to my own ob- 

 servations in the summer of 1886 upon the Muir Glacier, 

 Alaska, the central portions, a mile back from the front 

 of that vast ice-current, were moving from sixty-five to 

 seventy feet per day. These observations were taken with 

 a sextant upon pinnacles of ice recognizable from a base- 

 line established upon the shore. It is fair to add, how- 

 ever, that during the summer of 1890 Professor H. F. 

 Eeid attempted to measure the motion of the same glacier 

 by methods promising greater accuracy than could be ob- 

 tained by mine. He endeavoured to plant, after the method 

 of Tyndall, a line of stakes across the ice-current. But 

 with his utmost efforts, working inwards from both sides, 

 he was unable to accomplish his purpose, and so left un- 

 measured a quarter of a mile or more of the most rapidly- 

 moving portion of the glacier. His results, therefore, of 

 ten feet per day in the most rapidly-moving portion ob- 

 served cannot discredit my own observations on a portion 

 of the stream inaccessible by his method. A quarter of a 

 mile in width near the centre of so vast a glacier gives 

 ample opportunity for a much greater rate of motion than 

 that observed by Professor Reid. Especially may this be 



