KiLROE — The Shannon : its Course and Geological History. [91 



greatest stresses " to bring about bending and even crumpling and 

 shearing such as they illustrate. 



Perhaps it is not necessary to suppose liquefaction ; the fracture 

 and re-arrangement of ice-crystals under different degrees of pressure 

 in the mass would seem quite capable of accounting for the bending. 

 Hess appeals to Tresca's experiments regarding the effects of intense 

 pressure upon metals at ordinary temperatures ; and it would appear 

 we may take the molecular (or crystalline) re-arrangement of metals, 

 when flowing under pressure, to illustrate the readjustment of ice- 

 crystals under corresponding conditions. This being so, we should 

 C A B 



Fig. 1. 



expect conditions such as the following in glacier-flow. Take^^(fig. 1 ) 

 to represent an ice surface-plain, inclining slightly upwards towards B. 

 A C another, rapidly declining towards C, where the opening from a 

 valley admits of rapid expansion of the mass, and a corresponding rapid 

 lowering of the surface. Let be a very small ice-mass, a certain 

 distance h below the surface, and let h cji M he a function of M 

 expressing its tendency to spread under the pressure of the column 

 of ice, h. Take J/' and h' to represent, say, the adjoining mass and 

 its depth : the corresponding function in this case is h' cf> M'. Thus 

 Ji <f> M - h' (fi M' represents a tendency in M to move (which is not 

 counterbalanced by that oiM') in addition to the general movement of 



