THE FRESH-WATER LOCHS OF SCOTLAND. 
331 
western slope of Beinn Laoghal, a second passing through the hollow 
occupied by the loch of that name, and a third round the eastern slope 
of Beinn’s Tomaine. The stages in the gradual retreat of the mass of 
ice that moved down the valley of Loch Laoghal are clearly marked by 
a succession of moraine terraces, which enclose the small lochans shown 
on the chart to the east of Loch Creagach and Loch Slaim. 
Loch an Dithreihh is a rock basin lying in hornblendic and micaceous 
gneisses, whose strike is nearly north and south and nearly parallel to 
the direction of the lake. They are admirably exposed on the great <;rag 
on the east side of the loch. The solid rock is not exposed at the lip 
of the basin, but at a point in the stream about a quarter of a mile below 
the outlet at a height of 261 feet, the surface of the loch being 267 feet 
above sea-level, and the deepest part of the basin being 157 feet. 
Loch Syre, like many of the lochans east of Loch Laoghal, is sur- 
rounded with morainic deposits. 
Notes on the Biology of the Lochs of North Sutherlandshire. 
By James Murray. 
Tow-nettings were taken in seven of the lochs. These include three 
deep lochs (Hope, an Dithreibh, and Laoghal), two very shallow lochs 
(Chaluim and na Meide), while Loch Naver is intermediate. The 
biological phenomena are in accordance with those differences, the 
plankton of the deep lakes being relatively poor, and similar to that of 
great lakes in general, the shallow lakes having a large admixture of 
littoral forms. 
All the lochs were rich in algae, especially Desmids, including many 
of those conspicuous species of western type, alluded to by Messrs. 
West, which are so characteristic of the extreme north-western fringe 
of Europe. The northern species of Diaptomus — D. laciniatus, D. 
laticeps, and D. Wierzejskii — which are so widely distributed in the 
north of Scotland, Orkney, Shetland, and the western isles, and which 
are common in many lochs immediately adjacent, both to the east and 
south, are absent from most of the lochs of this district. D. laticcps 
is in Lochs na Meide and Naver, D. laciniatus in Loch na Meide only. 
D. gracilis is in six of the lochs, and in five it is the only species. 
In the short lists of organisms following the name of each loch, 
species of general distribution are omitted, only those being included 
which are interesting on account of their distribution or rarity. 
Loch Hope. — Leptodora, Baphnia hyalina (head rounded), Dia- 
phanosoma, Floscularia pelayica, Triarthra lonyiseta, Clathrulina 
