on the shores of Lough Mourne. 123 
the surface of the lake is accounted for by the lowering of the 
level of the waters before mentioned; and its position on the 
north-east shore is no doubt to be ascribed to the circumstance 
that south-west winds prevail at the season when the filaments 
to which the Diatomacee are attached, are loosened by the cold 
of autumn and winter. 
At the present level of the water in the lake, near the spot 
where the layer now mentioned is found, there does not appear 
to be any fresh deposit of a similar character. This may possibly 
be owing to the more abrupt shelving of the bank, not affording 
a resting-place for the floating weeds ; but on advancing towards 
the south and on the level strand of a little bay, there formed by 
a bend in the outline of the shore, a second deposit occurred 
evidently of a more recent formation. It was found covering 
the mud in a very thin stratum, and much more intermixed 
with earthy and other matters than the layer on the north-west 
shore. This layer is probably the result of accumulations made 
since the deepening of the outlet from the lake, and the date of this 
operation, and the comparative thickness of the layer itself, might 
possibly afford materials by which an estimate might be formed 
of the period occupied in the accumulation of the older deposit. 
The hurried nature of my visit did not permit me to make the 
inquiries necessary for such an investigation. No further deposits 
were found, nor were there any appearances of such on the western 
shore of the lake. 
As important in determining the character of the deposits 
found, I made a gathering of such living Diatomacee as were 
within my reach, and I now subjoin a list of the species, disco- 
vered on a careful examination of all the collected materials, 
adhering throughout to the nomenclature of Kiitzing in his 
‘Bacillarien oder Diatomeen.’ As a curious illustration of a 
“ multum in parvo,” I may mention that a drop which adheres 
to the point of a knife, dipped into water, holding the earth of 
the earlier deposit in suspension, will be found to contain nearly 
all the species mentioned below, and of some of these hundreds 
of individuals. 
I have marked (+) those species which were found living in 
the lake ; with one or two exceptions all the others were common 
to either deposit. In the older, or that from the north-east shore, 
the most conspicuous species and occurring in great abundance 
was Surirella splendida. The Epithemie were also exceedingly 
numerous. In the more recent deposit, Surirella splendida was 
in very small quantity, but its place was in some degree supplied 
by the beautiful Melosira arenaria, which I could not detect in 
the former. The Epithemia, which I have dedicated to one of 
my companions in a most agreeable excursion (whose reputation 
