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 Diatomacece 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 Diatomacece 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 (f) 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 Epithemice 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 Epit hernia, which I have dedicated to one of 

 my companions in a most agreeable excursion (whose reputation 



