THE BREAKING OF THE SHROPSHIRE MERES. 
61 
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 indistinguishable, and the water presents 
a sort of feculent opacity, accompanied with a dull, dirty, greenish 
hue. On lifting some of this in a glass, it seems, at first sight, 
quite transparent; but, on holding it up to the light, innumerable 
minute flocculi are seen floating through every part of . it, and 
producing a mottled cloudiness throughout the whole. On enquiry 
among my friends at Glaslough, I found that several theories were 
entertained respecting the green tinge of the lake, very wide of its 
true cause. According to one surmise, it was owing to some mineral 
impregnation, probably of a copper mine at the bottom of the water ; 
and another, equally unfounded, attributed it to the drainings of a 
tan-yard running from the town. At first I could only find the 
plant diffused through the water as above mentioned, but at length 
I discovered a wet ditch, extending from the lake into an adjoining 
field, and there it appeared swimming on the surface in large 
masses several inches in thickness, and above a foot and a half in 
length. That these masses were formed by an aggregation of 
filaments which had previously floated through the lake, but now, 
being freed from the agitation of the waves, were allowed to congre¬ 
gate in the motionless water, I would infer from the tendency they 
show, when undisturbed, to ascend to the surface. From the 
accounts I received, the green colour is evident in the lough 
throughout the year, and, if I may judge from my own observation, 
every drop of it is impregnated with the oscillatory filaments.” 
The name given to this alga was Oscillatoria arugescens. 
Herr Ferdinand Cohn, Professor of Botany in Breslau, writing 
to a German periodical, Hedwigia , in 1878, relates an interesting 
case that came to his knowledge. He says :—“ Though the 
appearance of the Wasserbluthe has often been observed and 
examined, very little is known of the causes from which it originates. 
Within the course of a few hours an alga so densely covers a vast 
extent of the surface of the water that it imparts to it a distinct 
colour—green, brown, or red. Sooner or later it disappears, 
either periodically or altogether. The only reason for this that 
can be assigned, apart from the extraordinary increase of the 
March, 1893. 
