102 VISCOUS THEORY OF GLACIER MOTION. [1845. 



But setting aside the attempt to render the sliding motion 

 of the entire glacier considered as a plane slab more easy, by 

 considering the motions of the parts instead of the motion of 

 the whole, we are led to notice the attempt to reconcile the 

 sliding theory to recent observation, by ascribing to the crevasses 

 of the glacier the important office of enabling it to accommodate 

 itself to the inequalities of its channel. 



Our object is, in this section, merely to state the view in 

 its most plausible form, which in the succeeding section we 

 shall controvert by experiments giving it a direct negative. In 

 the third portion of this essay we shall enter more at large into 

 the phenomena of crevasses, and mention other objections to 

 this hypothesis and every modification of it. 



According to this view, the friction of the ice against the 

 sides of the valleys will produce a dislocation of the glacier into 

 longitudinal stripes (as shown in Plate II. fig. 1.*), where a 

 transverse line W becomes by the irregular motions of the ice 

 distorted into the zigzag form hcc'h. Or if we suppose the 

 plasticity of the ice to be sensible, but that its action is accom- 

 panied with fractures, the abruptness of the angles of the figure 

 will be softened, as in the broken line Imm'l in the lower part 

 of the same figure. This latter hypothesis evidently merges into 

 the true plastic theory, when the part of the progression due to 

 the flexure of the transverse lines bears a large proportion to the 

 effect of the longitudinal slide, or more generally, when the 

 surfaces of sliding or yielding become greatly multiplied, when 

 the notched line will merge into a curve. 



The passage of the glacier through a gorge or contraction 

 is explained on the same view by fig. 2, where the resistance 

 of the sides having occasioned a series of parallel longitudinal 

 rents as before, the portion of the glacier beyond the limits of 

 breadth of the gorge BB' is supposed to be detained or embayed 

 whilst the intermediate columns slip through. 



* These figures and their interpretation are taken from Mr. Hopkins' First Memoir 

 in the Cambridge Transactions, vol. viii. part 1. A figure similar to the first is to 

 be found in a more recent paper by the same author in the Philosophical Magazine 

 for June 1845. 



