Ice and ifs Xatural History 267 



surrounded by light-coloured canals. In one piece, which 

 was much weathered, I counted 24 such grains in an area 

 of 9 square centimetres. In a slab which had not been lying 

 long, I counted 23 grains in an area of 150 square centi- 

 metres, giving an average area of 6*5 square centimetres per 

 grain ; the largest had an area of 12 square centimetres. In 

 another slab there was a very large grain which measured 

 7 centimetres in one direction and 4 centimetres at right 

 angles to it. In a slab in which the sun-weathering had 

 proceeded very far, I counted 1 13 grains in a disc of 5 centi- 

 metres radius, which gives o~6g square centimetre as the 

 average area per grain. 



In the absence of actual experience, one is apt to expect 

 a slab of lake-ice, when subjected to sun-weathering, to be 

 disarticulated into hexagonal columns ; but this expectation 

 is quite gratuitous. Ice may crystallise in a form bounded 

 by plane faces, according to the laws of its crystallographic 

 system if it has the freedom which it possesses when crys- 

 tallising out of an independent medium such as a saline 

 solution or air. But the foreign matter dissolved in fresh 

 water is present in so small quantity that what we have before 

 us is the solidification rather than the crystallisation of ice, 

 and each column as it tries to develop itself is interfered with 

 by its neighbour, and the resulting slab of ice is made up of 

 elementary prisms crowded together, but preserving parallelism 

 of crystallographic axis. 



Characteristics of an Advancing Glacier. In the month 

 of August 1895 I visited the valley of Chamonix, and had 

 the good fortune to find that the Glacier des Bossons was 

 advancing. This was particularly noticeable when crossing 

 the moraine on its eastern flank. The ice was everywhere 

 undermining it, and keeping it generally on the move. On 

 the western side, where the glacier terminated in several 

 points, these acted like ploughshares, in turning over the 

 detritus in front of them. The glacier stream escaped from 

 an Antrum, having a remarkably small entrance, about 2 

 metres high and 3 metres wide. 



In pursuance of certain experiments which I was making 



