Mr R. Adie on Ground- Tee. 247 



cient for ice-making as the somewhat similar one described as seen 

 on the Pentland Hills. These masses on the banks, no doubt assisted 

 by the power of a bright sun, broke off and fell into the stream, 

 where they formed a part of the floating ice seen passing down : being 

 loosely compacted together, they had often considerable thickness. 

 At the time it appeared to me that, as these passed down they had 

 furnished from their under surfaces, the ground-ice found among the 

 plants ; and when they ceased to pass, the ground-ice quickly disap- 

 peared. 



The frost slackened a little next day without thawing a thin co- 

 vering of hoar-frost in shaded places. The succeeding night was a 

 moderate frost ; and within forty-eight hours from the time I had 

 seen the stream choked with soft masses of floating-ice, I revisited 

 it, when there was little floating, and no ground-ice ; although in the 

 stagnant waters the ice coating had increased, all the moving waters 

 had cleared themselves. Temperatures, water of stream 33°, mud 

 of bed at the surface 36°, 6 inches deep 37°, air with a bitter frozen 

 fog 30°.* 



The quantities of scales of ice found on the banks of a stream, in 

 many places ready to drop in, through a severe night's frost follow- 

 ing a period of wet weather, is a fact well worthy of attention. To 

 me it at once accounts for the great masses of soft ice, Mr Esdaile 

 describes as coming from far up the country to Perth, being a cha- 

 racteristic of the commencement of a severe frost in the river Tay. 

 This floating-ice he also describes as true ground-ice ; but I believe 

 it would be more correct to hold that it is one of the sources from 

 which this kind of ice is derived. For other supplies of ice — crys- 

 tals to streams, there is the same nuclei which exist in stagnant 

 pools ; also the drift by the wind of snow or hoar-frost, and the ice- 

 pillars I have already noticed. 



The ground-ice I have seen has been described as consisting of 

 thin scales. Many of the published accounts represent the texture 

 as spiculse like the component parts of snow ; and this is generally Mr 

 Elliot's mode of characterising it for the Teviot. The velocity of the 

 current of the stream probably regulates these differences ; while, 

 from the observations above given, changes in the same locality may 

 be expected from the kind of weather which has immediately pre- 

 ceded the time of the ground-ice. Dr Davy's ! description for the 

 lake destrict, states the ice to be fine-grained, but he has noticed so- 

 lid ice in cakes, and on a few stones, under water, these are quite 

 exceptions to the general form of ground-ice, and may admit of ex- 

 planation through the force of the current transporting them from 

 the place of their formation at the surface. 



* During this fog, I remarked that a thermometer bulb warmed by the hand 

 and then exposed, got much fjooner coated with ice, than when exposed cold 

 and dry. 



t Edinburgh Philosophical Journal, vol. Ixxvii., p. 7. 



