260 Ice and its Natural History 



planes, which form the continuation of the corresponding 

 laminae of the parent crystal. This was well observed at 

 the end of August, 1895. Every night a thin skin of ice 

 was formed at the shallow end of the lake, where the ice-blocks 

 were collected. As the grains in a block of glacier-ice are 

 distributed quite irregularly, the water line of a floating block 

 necessarily cuts a great number of grains, all of which are 

 oriented differently. The ice which was formed during the 

 night along this line was oriented crystallographically by 

 the grain with which it was in contact and from which it 

 appeared to spring in continuation of its crystalline lamina;. 

 This produces a remarkable pattern of lines on the surface of 

 the lake-ice contiguous to a block of glacier-ice. 



Tyndall has described and figured the minute features 

 of the disintegration of the crystal under the absorption of 

 radiant heat. Similar and complementary features are ob- 

 served when ice is generated from an existing crystal under 

 the dissipation of heat. To do justice to them, however, 

 would require the services of a skilful, patient and resourceful 

 artist. 



The disarticulating and analysing action of the sun's rays 

 is not accomplished without selection and the expenditure of 

 energy. Accordingly we observe that one grain protects an- 

 other. The disarticulation into separate grains, although very 

 thorough near the surface of a glacier, does not penetrate far. 

 A stroke or two with an ice-axe reveals the fresh blue ice. 

 The analysis of the individual grain into crystallographically 

 oriented laminae can be particularly well studied in the Mer- 

 gelin See. It is only the grains that are exposed to the sky, 

 and above water, that are so analysed; and prolonged exposure 

 of this kind reduces a grain to the last stage of dilapidation. 

 The grains beneath the surface, whether of ice or water, are 

 almost completely unattacked. 



The importance of direct sky-light for the disarticulation 

 of glacier-ice into its constituent grains is very well seen in 

 the artificial grottos which are maintained at easily accessible 

 parts of most popular glaciers. One of the galleries in the 

 grotto of the Morteratsch glacier is represented in Fig. 3. It 



