452 NATURAL SCIENCE. June. 1894. 



by the eddies, and there, coming into contact with stones and 

 weeds, are collected and frozen together into a tangled mass of 

 spongy ice. It is probable that ice crystals are always present when 

 ground ice is being formed, they are specifically mentioned by 

 Knight, 5 by Eisdale,^ who thought that they originated in the air and 

 then fell into the water, and by Rae,7 while the only observation 

 which my limited opportunities have enabled me to make, tends to 

 show that the accumulation of small ice crystals independently 

 formed in the water of the stream is a most important factor in the 

 production of ground-ice. 



In May, 1888, I was encamped at Karzok, on the shores of the 

 Tso Moriri, at an elevation of close on 15,000 ft. above the sea. The 

 camp was pitched on the edge of a small oasis of cultivation, and the 

 irrigation channel, which supplied the fields, flowed not far from 

 the door of my tent. The night had been a cold one, and in the 

 morning, while the ground was still hard with frost, I noticed that 

 the water in the irrigation channel had risen and overflowed its 

 banks ; as this water was derived from the melting of snow on the 

 hills, it should have been at its lowest in the early morning, and the 

 rise of the water during the night made me look for the cause of so 

 unexpected an occurrence. I found that a sheet of semi-opaque, 

 whitish ground-ice had formed on the bottom of the channel and so 

 raised the level of the water, and that the ice was still growing. As 

 the depth of the channel was under a foot, the process was an easy 

 one to observe, and I was able to notice that the water was full of 

 minute crystals of ice, which were swept along by the current, and, 

 coming into contact with the surface of the ice on the bottom, 

 became entangled in the irregularly disposed crystals of which it was 

 composed and frozen into one solid mass with them. Owing to a 

 diversion of the stream, consequent on its rise of level, I was also 

 able to observe the gradual formation of a continuous sheet of ice. At 

 first the ice crystals accumulated against stones and weeds in the 

 bed, and principally on the up-stream side, as was observed by 

 Knight in 1816 ; but as the numerous small local clusters of crystals 

 grew in size they coalesced to form a continuous sheet with an 

 irregularly-mammilated upper surface. 



From these observations it would seem that the earliest theory 



proposed comes so near the truth that the neglect it has met with 



is not justified. The crystalHsing out of water reduced to or slightly 



below freezing point is doubtless a cause, and may in some case be 



the most important one in the formation of ground-ice ; but the 



process is aided to a much larger extent than is generally recognised 



by the entanglement and accumulation of ice crystals formed and 



floating in the water. 



R. D. Oldham. 



5 Phil. Trans., iSi6, p. 286. 



« Edin. New Phil. Journ., vol. xvii., 167-171 (1834). 



' Nature, vol. xxi., 538 (1889). 



