IS 12. 1 I'.MAUINO OF TIIK < H'-SKl! V ATluNS 1'1'oN KXISTlNd TIIICOIUKH. 31 



ice, remains sensibly vortical so long as it stands at all ; for 

 the velocity of the surface is sensibly the same as that at 10 or 

 20, or probably even 100 feet deep in most glaciers. It is only 

 near the bottom or bed that the velocity is materially affected, 

 as I have found also, that, in respect to breadth, it is in the imme- 

 diate neighbourhood of the sides that the velocity diminished 

 rapidly, and that, for half its breadth in the centre, the 

 velocity does not vary by more than from -j^ to -fa of its 

 amount. It is farther worthy of notice, that whenever a glacier 

 is of no great thickness, and, at the same time, highly inclined, 

 is, in circumstances calculated to produce a great difference 

 the motions of points of the glacier in a vertical line, 

 there the fissures are not transverse but radiated, as in almost 

 all glaciers of the second order, and, therefore, the fissures are 

 not liable to distortion. 



I might put it rather as a direct result of observation than as 

 ;i hypothesis, that the motion of a glacier resembles that of a 

 viscid fluid, not being uniform in all parts of the transverse 

 section, but the motion of the parts in contact with the walls 

 being determined mainly by the motion of the centre; but it 

 yet remains to be shewn what is the cause of the pressure which 

 conveys the motion, whether il, i,s the mere weight of the He.mi- 

 II 1 1 id mass, or the dilatation of the head of the glacier pushing 

 onwards. The answer to this question involves the fate of the 

 rival theories of Do Saussuro and De Charpcntier. 1 still 

 entertain the same difficulties with respect to both, which I have 

 stated in an article in the Edinburgh Review ; but these diffi- 

 culties amount, I think, to a proof of insufficiency, if taken in 

 connection with the observations which I have made this sum- 

 mer. On the one hand, if it were possible that the glaeier 

 could slide by the mere action of gravity in a trough inclined 

 only 3, or 4, or 5 degrees, it is probable that one of two things 

 would happen ; either it would slide altogether with an accele- 

 rated velocity into the valley beneath, or else it would move 

 by fits and starts, being stayed by obstacles until these were 

 overcome by the melting of the ice beneath, or by the aecumu- 



