The Theory of Glacier motion. loi 



which close up as the hinder field overtakes the one in front, 

 and the one in front pushes before it the earth as it advances/' 

 Our author writes very modestly, however, and confesses 

 that the subject is full of difficulty {Lettres Physiques^ etc. 

 The Hague, 1778, vol i. 140 — 142). 



De Saussure, to whom the sliding theory is generally 

 attributed, no doubt discovered and published it indepen- 

 dently, but later, in his work, Voyages dans les Alpes, of 

 which the first volume was published in 1779. Misstate- 

 ment of it I translate as follows : " Another cause which 

 prevents the excessive growth of the snow and ice is their 

 weight, which presses them more or less rapidly into the 

 valleys where the heat of the summer melts them. The 

 descent of the snow in the form of an avalanche is a known 

 phenomenon to which we shall return. That of the ice, 

 which is more gentle and generally with less noise, has been 

 less observed. Nearly all glaciers, as well of the first as of 

 the second kind, rest on inclined beds, and all those of more 

 than a certain size have beneath them, even in winter, 

 currents of water which flow between the ice and the bed 

 which supports it. It can be understood, therefore, that 

 these frozen masses, following the inclined bed on which 

 they rest, separated by the water from their attachment to 

 the ground and sometimes supported by the water, must 

 slide little by little and descend, following the inclination of 

 the valleys. It is this gradual but continuous sliding of the 

 ice on its inclined bed which moves it into the low valley." 

 These sentences contain what De Saussure had to say 

 about the motion of glaciers, and it will be seen that both he 

 and his predecessor, Gruner, contented themselves with the 

 supposition, to use the words of Principal Forbes, " that the 

 mass of the glacier is a rigid body sliding over its trough or 

 bed in the manner of solid bodies." 



This view was maintained by De Saussure's followers, 

 notably by Ramond, Kuhn, etc., who all apparently treated 

 G 



