ALG.IL. 139 



there was in some places merely a little scum, which, 

 excepting its very pale greenish tinge, resembled pre- 

 cisely the appearance remaining on the surface of 

 water in which ice has been dissolved. Towards the 

 edge of the lake there were in some places gelatinous 

 tufts of a pale blue colour, in one place crowded 

 tocrethcr in a mass which covered an area a few 

 yards in extent. The portion nearest the edge had, 

 apparently from decay, become ferruginous, and 

 strongly tinged with rust colour the paper on which 

 it was placed, but with the greatest pains I could 

 hardl}^ obtain a trace of the blue colour. The masses, 

 both blue and ferruginous, were very slippery to the 

 touch, about an inch in thickness, and of considerable 

 consistence, and, on being lifted out of the water in a 

 wire-gauze net, remained there without diminution 

 by dripping off, or otherwise ; their weight, too, was 

 great. When brought near they had somewhat of 

 the offensive smell of water in which flax has been 

 steeped, and at a short distance from, one part of the 

 lake this disagreeable odour was sensibly perceived. 

 About seventy days after the first visit the algs had 

 entirely disappeared from the lake, the water through- 

 out its depth as well as at the surface being clear and 

 pure. The conclusions arrived at were, that the alga 

 undergoes no change whatever, either in size or other- 

 wise, from its first appearance as a colouring matter, 

 until about three months afterwards, when decompo- 

 sition ensues, and it is utterly dissolved. The speci- 

 mens obtained of the alga were invariably of similar 

 breadth, and rarely presented more than four spiral 

 turns, and about one-fiftieth of an inch in length, at 



