-492 ON THE STRUCTURE OF GLACIER ICE 



layer," however, is no less certain, and inasmuch as this layer is 

 continually and rapidly wasting away at its surface, it must be as 

 constantly reformed from the solid glacier ice beneath. 



The fact observed by Prof Agassiz, that under a moraine (that is, 

 where covered and protected by stone and gravel) the superficial ice 

 is of the same character as the deep, suggested the idea that the 

 superficial layer is the result of the operation of atmospheric influences ; 

 and that just as a bed of impervious rock becomes broken up into 

 fragments, separated by permeable interstices, down to a certain 

 depth wherever it is exposed to the atmosphere, so the glacier ice 

 when left unprotected undergoes a similar weathering and disintegra- 

 tion. I submitted this notion to the test of experiment in the 

 following way : — Not far from the upper end of the iVloraine du 

 Noire, and on one bank of a stream which cuts its way down the 

 Glacier du Gdant, I cleared away the superficial layer and cut out a 

 block of the deeper ice, which was then divided into two equal 

 portions of irregular cuboidal form, and about 8 inches in the side. 



The logwood infusion was poured on both of these, and was 

 retained only by such portions of the superficial layer as had been 

 allowed to remain. Water poured on to the blocks ran off them as it 

 would run from marble or glass, sinking only into the remains of the 

 superficial layer. I then placed the two blocks side by side, on an 

 elevated ridge of the glacier, with their natural upper faces turned 

 towards the sun, at this time (1.15 P.M.) shining brightly ; the one 

 block I left without protection, while the other was just covered by a 

 -stone of 4 or 5 inches in thickness, resting upon its upper face. At 

 1.40, that is to say in less than half an hour, I removed the block of 

 -Stone and poured the infusion over both pieces of ice. The covered one 

 could be as little infiltrated as before, while the face of the uncovered 

 became at once beautifully injected, the fluid instantly running into a 

 network of little superficial fissures which had developed themselves, and 

 out of which the infusion could be only partially extracted by washing. 



Both pieces of ice were well washed, and the stone was replaced 

 on the one, while the other was left uncovered as before. 



In the course of the ensuing half-hour I examined both blocks 

 several times. The covered ice remained unchanged ; but in the 

 uncovered, the fissures extended further and further into the mass, 

 which gradually assumed throughout the granular aspect of the 

 superficial layer. Water poured on its surface soaked into it imme- 

 diately, and a small quantity of the infusion spread out, the moment 

 it reached the block, in the most beautifully ramified figure through 

 the fissures. Particularly large and apparent fissures could thus be 



