332 REV. JAMES FARQUHARSON ON THE ICE 



as will be afterwards seen. It occurred to M. Hugi, as quoted by M. Arago, in the 

 Aar, on the 16th February 1827, with a west wind, after the river had been com- 

 pletely open on the 15th ; and one of Mr. Eisdale's correspondents ascribed its oc- 

 currence in one particular instance, which he related to him, to the prevalence of a 

 very sharp north-east wind, which had blown during the night of its formation. 



The following observations were made in ihe rivers Don and Leochal. The former, 

 having an easterly course, is about 120 feet broad, and a foot or two deep at the 

 shallows and fords. The latter, one of the small tributaries of the former, having a 

 northerly course, is about 20 feet broad, and a foot deep at the shallows. Both rivers 

 possess a like character of very clear water, and alternating rapids and pools. The 

 rapids in the Don are reaches, where the water falls two or three, or more, feet, from 

 a higher to a lower level, within a distance of fifty or a hundred, or sometimes two or 

 three hundred, yards. They are generally impeded with many large stones, some of 

 them projecting above the water. The depth varies greatly, but seldom exceeds two 

 or three feet. The pools between the rapids are on an average much longer reaches, 

 in which there is little fall, and a greatly diminished velocity of the stream, which 

 often, in them, flows so equably as to give rise to no ripple on the surface. They too 

 have in them large stones, but fewer in number. The depth in them too varies 

 greatly, from two or three to four or five feet. The rapids and pools in the Leochal 

 are of a similar kind, but both much less deep in this smaller stream. The bed of 

 this river has however, on the whole, a steeper descent, and owing to this there is 

 more broken water and spray in the rapids. The character of alternating rapids and 

 pools, in both streams, is owing to the varying hardness of the granitic and micaceous- 

 schistose rocks in which their beds are formed. Where the rocks are hard, there is 

 a rapid ; where more friable, a pool. In the parts of the rivers observed, the original 

 rocks themselves do not anywhere form the immediate bed of the stream. That, to 

 the depth of two or three, or more, feet, is composed of the debris of these rocks, 

 broken up and sometimes much waterworn, and reduced to the size of a very large 

 gravel, by the action of the stream, but not so small as to deserve to be named sand. 

 No part of the bottom is muddy. 



On the night between the 31st of December 1834 and the 1st of January 1835, 

 after the mean temperature of the air had continued for three days at 47° Fahr., and 

 when there had been little frost in the season before, there commenced a hard frost, 

 with a calm and perfectly cloudless sky, which continued with little abatement till 

 the 5th of January, at 10 a.m. On the night between the 3rd and 4th, the tempe- 

 rature of the air was 23° Fahr. ; and on the 4th, the bottoms of the rapids in the 

 Leochal were seen coated in some places with silvery cauliflower-shaped clusters of 

 ground-gru. I neglected at this time to examine the temperature of the water. 



Between the 4th and 5th, the temperature of the air was down to 19° Fahr. ; and 

 on the 5th I examined the Don and the Leochal along half a mile of each, beginning 

 the examination at half-past 8 o'clock a.m. The examination began at the bridge of 



