72 Mr. H. H. Howorth on 



characteristic of granulation. As Messrs. McConnell and 

 Kidd say in their recent paper, " Glacier ice is a sort of con- 

 glomerate formed of glacier grains ( G/etscherkorner), differ- 

 ing, however, from a conglomerate proper in that there is 

 no matrix, the grains fitting each other perfectly. In the 

 winter, at any rate, the ice on the sides of the glacier caves 

 looks quite homogeneous. But, when a piece is broken off 

 and exposed to the sun's rays, the different grains become 

 visible to the naked eye, being separated probably by thin 

 films of water. Though the optical structure of each grain 

 is found under the polariscope to be perfectly uniform, the 

 bounding surfaces are utterly irregular, and are generally 

 curved. The optic axes too of neighbouring grains seem 

 arranged quite at random " {Proceedings, Royal Society y 



XLiv. 333—334). 



M. Forel, who has devoted much labour to the elucidation 

 of the internal structure of glaciers, thus defines this curious 

 feature of glacier ice : " The mass of the glacier is formed of 

 an agglomeration of crystals pressed against each other, and 

 so interlocked and intertwisted that it is difficult to separate 

 them, and forming a piece of compact masonry of ice 

 crystals. The crystals are irregular in shape, some with 

 their parts curved, and their axes apparently lie in all direc- 

 tions. These glacier crystals it has been shewn {vide infra) 

 grow from the size of a small lentil near the neve to that of 

 a hen's ^gg at the base of the glacier." M. Forel succeeded 

 in imitating glacier ice by alternately allowing snow to freeze 

 and pouring over it water above 0° centigrade in tempera- 

 ture. In this way, ice of the granular texture of glacier 

 ice was produced, and it apparently follows that a glacier 

 is formed by the periodical melting of its surface by 

 the sun, rain, etc., and its subsequent freezing, a process 

 assisted by the presence of the two containing walls of the 

 valley in which it lies. It is most important in this discussion 

 to remember what most of those who have treated of glacier 



