230 FRAGMENTS OF SCIENCE 



times the weight of the glacier not only to a white heat, 

 but to its point of fusion. If, as I have already urged, 

 instead of being filled with ice, the valleys of the Alps 

 were filled with white-hot metal, of quintuple the mass of 

 the present glaciers, it is the heat, and not the cold, that 

 would arrest our attention and solicit our explanation. 

 The process of glacier making is obviously one of distil- 

 lation, in which the fire of the sun, which generates the 

 vapor, plays as essential a part as the cold of the moun- 

 tains which condenses it. 1 



It was their ascription to glacier action that first gave 

 the parallel roads of Glen Hoy an interest in my eyes; and 

 in 1867, with a view to self-instruction, I made a solitary 

 pilgrimage to the place, and explored pretty thoroughly 

 the roads of the principal glen. I traced the highest road 

 to the col dividing Glen Roy from Glen Spey, and, thanks 

 to the civility of an Ordnance surveyor, I was enabled to 

 inspect some of the roads with a theodolite, and to satisfy 

 myself regarding the common level of the shelves at oppo- 

 site sides of the valley. As stated by Pennant, the width 

 of the roads amounts sometimes to more than twenty yards; 

 but near the head of Glen Roy the highest road ceases to 

 have any width, for it runs along the face of a rock, the 

 effect of the lapping of the water on the more friable por- 

 tions of the rock being perfectly distinct to this hour. 

 My knowledge of the region was, however, far from com* 

 plete, and nine years had dimmed the memory even of the 



1 In Lyell's excellent "Principles of Geology," the remark occurs that 

 "several writers have fallen into the strange error of supposing that the glacial 

 period must have been one of higher mean temperature than usual." The 

 really strange error was the forgetfulness of the fact that without the heat the 

 substance necessary to the production of glaciers would be wanting. 



