108 THE FOEMS OF WATER IN 



say to-day. A few days or weeks hence this slice will 

 have been carried down, and because the centre moves 

 more quickly than the sides it will not remain straight, 

 but will bend into the form s' t\ 



273. Supposing t i to be a small square of the 

 original slice near the side of the glacier. In its new 

 position the square will be distorted to the lozenge- 

 shaped figure t' i'. Fix your attention upon the diagonal 

 t i of the square ; in the lower position this diagonal, 

 if the ice could stretch, would be lengthened to t' %'. 

 But the ice does not stretch ; it breaks, and we have 

 a crevasse formed at right angles to t' i'. The mere 

 inspection of the diagram will assure you that the 

 crevasse will point obliquely upwards. 



274. Along the whole side of the glacier the quicker 

 movement of the centre produces a similar state of 

 strain; and the consequence is that the sides are 

 copiously cut by those oblique crevasses, even at places 

 where the centre is free from them. 



275. It is curious to see at other places the transverse 

 fissures of the centre uniting with those at the sides, 

 so as to form great curved crevasses which stretch 

 across the glacier from side to side. The convexity of 

 the curve is turned upwards, as mechanical principles 

 declare it ought to be. (See sketch on opposite page.) 

 But if you were ignorant of those principles, you would 

 never infer from the aspect of these curves the quicker 

 motion of the centre. In landslips, and in the motion 



