THE FRESH-WATER LOCHS OP SCOTLAND. 
191 
north-east and south-south-west fault skirting the eastern shore, 
whereby the Torridon Sandstone has been thrown down against the 
Archaean floor on the east side. A glance at the map will show how 
the contour-lines run parallel to that fault and close to the shore, 
and that the deepest sounding, 153 feet, is not far from the line of this 
dislocation. 
Loch Urigill and Loch Maol o’ Ghoire are shallow rock-basins in the 
Cambrian limestone, the erosion of which may be partly due to 
solution. ’ 
Loch Borralan lies along the line of a consequent valley, near the 
headwaters of the river Kirkaig, and probably not far from the 
original axis of uplift in early Palaeozoic times. It is a shallow rock- 
basin, floored by igneous rocks which belong to the igneous mass of 
Cnoc na Sroine, with some drift along its margin. 
From the evidence now adduced, it is obvious that the plateau of 
Archaean gneiss with its intrusive dykes is dotted over with lakes of 
various sizes, which, with the exception of the lower part of Loch 
Assynt, are of moderate depth. Indeed, most of them are shallow 
basins, which reflect the varying types of gneiss and intrusive dykes 
and their subsequent deformation. It is, no doubt, true that the 
numerous shear-lines and faults of pre-Torridonian age that traverse 
the Archaean plateau have determined to some extent the features of 
these lakes; but we are, nevertheless, of opinion that the evidence 
taken as a whole is in favour of the theory that they have been mainly 
produced by the erosive action of ice. 
Notes on the Biology or the Lochs in the Assynt District. 
By James Murray. 
Only an incomplete sketch can be given of the biology of this 
district, as collections of plankton were made in only twelve out of the 
twenty lochs surveyed. Loch Assynt is the largest loch in the district, 
but four others, viz.. Lochs Lurgain, Skinaskink, Bad a’ Ghaill, and 
Owskeich, are moderately large and of considerable mean depth, so 
that they fall to be classed rather with the large lochs than with 
the small ones. The remainder are small or of low mean depth. 
The fauna of the plankton was very uniform throughout these lochs, 
differing chiefly in the presence in some of them of one or other of the 
northern species of Diaptomus, D. Wierzejsldi, L) . laciniatus, in the 
Daphnia being D. lacustris in some and D. galeata in others, and in 
the greater abundance of Rotifera and Rhizopods in the shallower 
lochs. Though the three common Scottish species of Diaptomus were 
