Mr. E. D. Oldham on the Modulus of Cohesion of Ice. 247 



motion. Such an ice-cap may have existed, and under favour- 

 able circumstances may have had some motion ; but if so, the 

 motion was confined to the upper layers, for the lower portion 

 must have been landlocked and stagnant. 



This note has already run to some length; so I shall conclude 

 by pointing out: — that the figures given above are not meant 

 to represent what a glacier actually can do, but the very outside 

 limit of what it could possibly do, and, as such, a very large 

 discount may be taken from them without altering their truth ; 

 that they will hold good on any theory of glacier-motion, for 

 the resistances of friction and gravitation will remain ; and 

 that the points I claim to have proved are as follows : — 



1. That no lake-basin exceeding 700 feet in depth or 5 miles 

 in length could possibly owe its origin to glacial erosion, 

 though the true limits are probably not one tenth of these 

 quantities. 



2. That no glacier could be pushed en masse over a plain 

 for more than 5 miles. 



3. That, consequently, no ice-cap could travel en masse over 

 large areas independently of the conformation of the ground 

 over which it travelled. 



January 25, 1879. 



PS. — Since writing the above, it has been pointed out to 

 me that it is hardly justifiable to apply the formulas of rigid 

 dynamics to the case of a body like ice, which, when moving 

 in large masses, assumes many of the appearances of a liquid 

 in motion. I may therefore point out that the idea in the 

 above paper is that, as soon as the resistance offered by fric- 

 tion rises to that point at which it would prevent all motion in 

 the glacier if the glacier behaved as a perfectly rigid body, 

 that point gives a limit beyond which it would not be possible 

 for any motion of the base of the glacier over its bed to take 

 place. 



Mr. Robert Mallet authorizes me to state that, according to 

 experiments made by Professor Phillips, the modulus of ice is 

 reduced to almost nothing by the presence of interstitial mois- 

 ture ; so. that if, as is generally supposed to be the case, glacier- 

 ice is permeated by interstitial moisture, the power of a glacier 

 in scooping out lake-basins would be reduced to almost no- 

 thing. 



Rugby, Feb. 15, 1879. 



