EXPERIMENTS ON THE PLASTICITY OF ICE. 
163 
between the rival theories was easy, and that it was only necessary to place a series 
of marks in a right line transversely to the glacier, and observe whether they were 
displaced by an imperceptible flexure, or whether they slid past one another by 
sudden dislocations. 
Such a proof was independent of any assertion as to the existence or not of such 
fissures as those contended for, about which different opinions might be formed, 
especially as they might be asserted to exist although invisible to the eye. Being 
satisfied in my own mind of the non-existence of such fissures wherever the ice is not 
violently dislocated and descends a steep place in a tumultuous manner (which, as 
already mentioned, is not the case which we consider), I had no hesitation in pre- 
dicting that the result of the experiment would be confirmatory of my theory, and 
contradictory of the other; that the transverse line would be found to become a 
continuous curve, and that no other system of fissures could be found in the glacier 
satisfying the mechanical postulate of the greater velocity of the central parts of the 
glacier, than the ribboned structure of the ice, which I had already pointed out as 
resulting from a forced separation of the semi-rigid ice, at a vast, though finite, 
number of points in the breadth of the glacier, and which I showed to exist exactly 
in the direction required for releasing the mass from the tension induced by the 
gravity of its parts. 
Having gone to Chamouni a few days later, I looked out for a place where the ice 
should be as compact as possible, wholly devoid of open fissures, and if possible con- 
tinuous up to the bank. This latter condition I found it impossible to fulfil on the Mer 
de Glace, at least without ascending to the neve, which might be objected to as less rigid 
than the glacier proper. The former condition was well-satisfied in a sort of bay on 
the west side of the Mer de Glace between the Angle and Trelaporte, exactly under the 
little glacier of Charmoz. The part adjoining the western shore of the glacier is in- 
deed highly crevassed, and therefore unfit for this experiment ; but at the distance of 
fifty or sixty yards from the moraine it becomes remarkably flat and compact for a 
space of about seventy yards in width, and several hundred yards in length, throughout 
which space there is not a single open crevasse. Now this compact area of ice pre- 
sents the veined structure in a nearly longitudinal direction, with a degree of delicacy 
and distinctness not to be found in any other part of this glacier (as I had already re- 
marked in my Travels, p. 159), and it contains no other trace of a system of longitu- 
dinal fissures or lines of separation of any kind, which could render mechanically 
possible the distortion of this flat compact surface of so great an extent. Now I have 
always observed that the veined structure near the side of a glacier is best developed 
where the ice is least crevassed. or the continuity of the mass most perfect ; a fact 
stated and referred to its true cause from the first date of my speculations on the origin 
of the blue veins, in the following words : — “ The veined structure invariably tends to 
disappear when a glacier becomes so crevassed as to lose horizontal cohesion, as when 
it is divided into pyramidal masses. Now this immediately follows from our theory ; 
