AQUATIC COLEOPTERA OF THE OUTER HEBRIDES 13 



THE AQUATIC COLEOPTERA OF THE 

 OUTER HEBRIDES. 



By Frank Balfour Browne, M.A. (Oxon. et Cantab,), F.R.S.E., 

 F.Z.S., Lecturer in Entomology in the Department of Zoology, 

 University of Cambridge. 



The Outer Hebrides are a series of islands near the western 

 edge of the continental plateau, and separated from the 

 mainland by a channel of water about 50 fathoms in depth, 

 and about 26 miles in width. The island of Skye is, how- 

 ever, situated between the mainland and some of the islands, 

 and the width of the "Little Minch" between North Uist 

 and Skye is only about 17 miles; and since Skye itself is at 

 one part, by Lochalsh and Kyle Rhea, within half a mile of 

 the mainland, the Outer Hebrides are not very markedly 

 isolated. 



The islands are composed of Archean rock — Lewisian 

 gneiss — except for a very small portion on the east of Lewis, 

 in the neighbourhood of Stornoway, where there is some 

 Old Red Sandstone, and the geological structure, especially in 

 the mountainous parts, gives a very characteristic appear- 

 ance, so well known all through large tracts of the western 

 highlands of Scotland, where the bare rock protrudes amidst 

 patches of peaty soil covered with heather and typical bog- 

 land grasses. 



One peculiarity of most of the islands is the great number 

 of lochs and lochans which they contain, the majority of these 

 being rock basins, supposed to have been gouged out by the 

 glaciers of the Great Ice Age, but some are mere peat-holes 

 of various sizes, some quite large others small, produced, 

 apparently, by the rotting away of an area of peat upon 

 a more or less level patch of ground. There is thus no 

 scarcity of fresh water on the islands, but there are, of 

 course, no extensive river-systems even in the island of 

 Lewis, though small streams are in plenty. 



In one or two earlier papers on the water-beetles of the 

 western Scottish isles, I have made some remarks on the 

 Britannic distribution of this group of insects, and it has 



