246 Mr R. Adie on Ground- Tee. 



portion of this stream is a wide slow flowing ditch, as much exposed 

 to the elements as the surface of the adjacent sea. In the second 

 week of December 1846, I found abundance of ground-ice, on the 

 third day of a moderate frost, assisted by a very dry wind. The 

 temperature in the stream was 32° exactly; the air in sun and wind 

 35°, wet bulb 32°. The ice consisted of thin transparent scales, lodged 

 in large quantities among the plants; some of these plants, attached 

 to the bottom by thin slender stems, as they waved and turned about 

 in the current, had gathered spherical masses of loosely compacted 

 scales of ice, many of the spheres being 6 inches beneath the sur- 

 face ; when the stem which served to moor them was broken, they 

 immediately rose to the surface and floated along : this process of 

 breaking the moorings was going on spontaneously to a considerable 

 extent. In the last week of December I again visited this locality, 

 after a sharp frost of only 24 hours' duration ; before mid-day large 

 masses of loosely compacted ice, composed of numerous scales and 

 thin surface-formed pieces were floating down ; and in the place 

 where the ground-ice was before found, these masses stretched over 

 the whole stream, here 17 feet wide, choking it ; so that the new 

 arrivals of fresh masses brought down by the current, descended with 

 the water and passed underneath, rising to the surface after the bar- 

 rier was cleared. I was anxious to examine the plants near this 

 place, but the depth and dark colour of the water rendered it im- 

 possible to see any of them. Farther up the stream there was ground- 

 ice in a few favourable places. Temperature of water 32 "2° ; air in 

 sun and wind 35°; wet bulb 31-5°; mud of bed of stream 34°. 

 Before 3 p.m. most of the floating masses of ice had passed down, and 

 the surface of the stream became remarkably open, the choked part 

 was clear for half its width, and I was surprised to find, that on the 

 plants where a little before I had seen the largest portion of ground- 

 ice there was now none. Shortly after three o'clock, the sun be- 

 coming obscured by a horizon cloud, and the wind dying quite away, 

 the temperature of the air sunk rapidly to 25*5°, where it was not 

 stationary 15'. I suppose this severe cold caused a thin veil of cloud 

 on the ground, which checked radiation, for the thermometer rose to 

 near 30°, and continued steady so long as day light sufficed to read 

 it. 



On examining some of the ice fished up from the bed of the 

 stream, I found it composed of clusters of scales frozen together as 

 if radiating from a centre ; searching the banks, I found masses of 

 similar clusters which appeared to have been formed in the follow- 

 ing manner. From late rains the water stood high; at the beginning 

 of the frost, a pellicle of ice was formed along the edges adhering to 

 them. In so flat a district the frost appears rapidly to diminish the 

 supply of water, and the surface of the stream had gradually lowered, 

 leaving the pellicle attached to the banks with an intervening space 

 filled up with clusters of scales ; this process appeared to be as effi- 



