ANNALS 



OP 



NATURAL HISTORY. 



I. — On a new Oscillatoria, the colouring substance of Glas- 

 lough Lake, Ireland. By James L. Drummond, M.D., 

 Professor of Anatomy in the Royal Belfast Institution, &c. 



XxAVING in the month of June last paid a visit to a friend 

 resident at Glaslough, in the county of Monaghan, I embraced 

 the opportunity of inquiring into the origin of the name of 

 that place. It is a small town built on the borders of a lake, 

 which occupies an area of about one hundred acres in extent, 

 and from it the town has its name. Glas-lough signifies in 

 the Irish language " the green lake," an appellation given to 

 it from time immemorial, on account of the hue of its waters, 

 which exhibit a green tinge equal to, or exceeding in intensity, 

 that of the sea, though it is not at all times equally striking. 



The opposite banks of the lake, which are high but not 

 rocky, are thickly clothed with a wood of noble trees, and on 

 my first seeing this beautiful sheet of water I was inclined to 

 suspect that its green colour might arise simply from the re- 

 flexion of the rich foliage on its surface. On further inquiry, 

 however, I ascertained that the colour resided in the water it- 

 self, and was owing to what I believe is an undescribed Os- 

 cillatoria. 



When a little of the water is lifted in the hand it seems per- 

 fectly transparent, and it appears equally clear at the edges of 

 the lake, in a depth of not more than a few inches, and there 

 the pebbles at the bottom show perfectly distinct, without any 

 intermediate cloud to obscure them. But at a depth of two 

 feet the bottom is undistinguishable, and the water presents 

 a sort of feculent opacity, accompanied with a dull, dirty, green- 



Ann. Nat. Hist. Vol. 1. No. 1. March 1838. b 



