266 Mr. J. T. Buchanan [May 8, 



Ueber das Wesen der GletscJier. All the changes which we witness tak- 

 ing place on the incline between the most elevated neve and the lowest 

 extremity of the glacier in the valley, are repeated on the vertical, 

 between the upper and the under surfaces of the neve and the glacier. 

 In both directions we observe greater age and more definite develop- 

 ment of the mass. Further, what we observe in both these directions 

 we observe also in the individual grain. The older kernel of the 

 neve is compact and blue like the lower glacier, while the white 

 spongy rind on the outside is more of the nature of snow, like the 

 highest neve, and passes by layers into the compact central grain. 

 Also in the case of the individual grain, the nucleus or kernel is the 

 first and oldest, and only by continued development does the rind 

 shape itself and gradually pass into the mass of the nucleus and so 

 become a glacier-grain, which then continues its development as the 

 glacier itself continues its own -development. In these relations lies 

 the foundation of the whole natural history of the glacier. It will 

 be observed that eighty years ago Hugi held very modern ideas on 

 the subject of development. 



The Grain of Lake Ice. — It is not glacier ice alone which suffers 

 disintegration when exposed to a powerful sun. Lake ice behaves in 

 a similar way. Beautiful examples of this can be seen in Alpine seas 

 every winter. During the harvesting of the ice from the lake, the 

 blocks often lie for a day or more before they are carted away to the 

 ice houses. Occasionally some of them get overlooked and remain 

 for many days exposed to the powerful sun of February, while main- 

 taining the low temperature of the air usual in that month. No 

 melting takes place ; but, after even a few hours' exposure to the sun, 

 the block shows the figure of its grain in development. It is being 

 etched by the sun's radiation. 



The grain of lake ice has a very different appearance from tliat of 

 glacier ice, but both are individual crystals. The difference in their 

 appearance is to be traced to the difference of treatment which they have 

 received during their existence. The glacier grains have been practi- 

 cally rolhng over each other during their descent, while those of the 

 lake have established themselves at right angles to the surface of the 

 water and have remained there. So long as the ice is increasing in 

 thickness, the temperature of its upper surface is very low. It is 

 perfectly transparent, and its surface is smooth, dry and polished like 

 glass, and it shows no trace of crystalline figure. AVhen the ice is 

 undisturbed, this develops itself only at the end of the season when 

 the thaw sets in. Then the whole ice sheet rises to its melting tem- 

 perature and is at the same time exposed to the direct radiation of the 

 sun. This produces disarticulation of the ice into groups of vertical 

 prisms, which are then floating independently : they are kept together 

 only by crowding. Ice in this state is said to be rotten ; and it will 

 be recognised that, however thick the ice sheet may be, when it gets 

 into this condition, it is dangerous. In the neighbourhood of the 



