1842.] PERMANENCE OF THE " MOULINS." 29 



the ever- varying state of its aggregation and subdivision. In 

 a glacier, like the Mer de Glace of Chamouni, which presents a 

 great many and well-marked "accidents" of surface in its 

 different parts, it is yet perfectly well known, that, though 

 continually moving and changing, the distribution of these 

 " accidents" is sensibly invariable. Every year, and year after 

 year, the water-courses follow the same lines of direction, their 

 streams are precipitated into the heart of the glacier by vertical 

 funnels called "moulins" at the very same points; the fissures, 

 though forming very different angles with the axis or sides of 

 the glacier at different points of its length, opposite the same 

 point are always similarly disposed, the same parts of the 

 glacier, relatively to fixed rocks, are every year passable, and 

 the same parts are traversed by innumerable fissures. Yet the 

 solid ice of one year is the fissured ice of the next, and the very 

 ice which this year forms the walls of a " moulin," will next year 

 be some hundred feet farther forward and without perforation, 

 whilst the cascade remains immovable, or sensibly so, with 

 reference to fixed objects around. All these facts, attested by 

 long and invariable experience, prove that the ice of the glaciers 

 is insensibly and continually moulding itself under the influence 

 of external circumstances, of which the principal, be it remarked, 

 is its own weight affecting its figure, in connection with the 

 surfaces over which it passes, and between which it struggles 

 onwards. It is, in this respect, absolutely comparable to the 

 water of a river, which has here its deep pools, here its constant 

 eddy, continually changing in substance, yet ever the same in 

 form. 



With reference to the yet more essential modifications of 

 structure, I mean the veined structure which I formerly de- 

 scribed ; I shewed in my last letter, that it is equally mutable 

 and subjected to the momentary conditions of external restraint ; 

 and that, far from being an original structure in the higher part 

 of the glacier, variously modified in its subsequent course, but 

 never annihilated, it owes its existence at any moment to the 

 conditions of varying velocity in different parts of the transverse 



