THE FRESH-WATER LOCHS OF SCOTLAND. 
283 
The loch is a flat-bottomed shallow basin, 45 per cent, of the lake-floor 
being covered by more than 5 feet of water. The temperature of the 
surface water on the date of the survey was 54°-8 Fahr., while a 
reading at the bottom in 7 feet gave 55°’0. 
The particulars regarding the lochs in the Conon basin are collected 
together in the table on p. 282 for convenience of reference and com- 
parison. From this table it will be seen that in the sixteen lochs under 
consideration, which cover an area of over 11 J square miles, nearly 
2200 soundings were taken, or an average of 188 soundings per square 
mile of surface. The aggregate volume of water contained in the 
lochs is estimated at nearly 30,000 millions of cubic feet, and the 
area draining into them is over 366 square miles, or 31 J times the area 
of the lochs. 
Notes on the Geology of the Conon Basin. 
By B. N. Peach, ll.d., f.r.s., and J. Horne, ll.d., f.r.s. 
The rock groups entering into the geological structure of the Conon 
basin and the area including Strath Glass and Strath Rusdale, north 
of Ben Wyvis, belong to the crystalline schists and the Old Red 
Sandstone. A line drawn from a point in Strath Rusdale above Ardross 
Castle, south-west by Eileneach in Strath Glass, Achterneed station, 
the Falls of Rogie, and across the Conon to Glen Orrin above Muirtown 
House, roughly marks the boundary between the metamorphic rocks to 
the west and the Old Red Sandstone bordering the Cromarty firth. 
It will thus be seen that the crystalline schists form not only the greater 
part of the basin, but also the highest and wildest territory. 
From the researches of the Geological Survey, extending over the 
greater portion of the area under description, it would appear that the 
metamorphic rocks may be arranged in two divisions ; (1) a group of 
acid, basic, and ultrabasic rocks, resembling certain types of Lewisian 
gneiss of pre-Torridonian age along the western seaboard of Sutherland 
and Ross; (2) the Moine series, representing altered sediments and 
including the main subdivisions, (a) granulitic quartz-schists or quartz 
biotite granulites, (b) flaky muscovite biotite schists or gneiss frequently 
garnetiferous, and passing into flaggy mica-schists (politic schists). 
Though the group of rocks of Lewisian type comprises certain acid 
granulitic gneisses that closely resemble the quartzose members of the 
Moine series, yet their dominant feature is the alternation of acid and 
basic materials in the form of biotite and hornblende gneisses. With 
