306 
BATHYMETRICAL SURVEY OF 
feet of water is about 66 acres, or 50 per cent, of the total area of the 
loch, while that covered by more than 25 feet of water is about 4 acres, 
or 3 per cent. Temperature observations taken in the deepest part of 
the loch at 1.30 p.m. on the date of the survey showed little variation, 
the reading at the surface being 52°*6 Fahr., at 20 feet 52°T, and at 
30 feet 52°'0. 
The particulars regarding the lochs of the Shin basin are collected 
together in the table on p. 305 for convenience of reference and 
comparison. From this table it will be seen that in the eleven lochs 
under consideration, which cover an area of over 12 square miles, 
nearly 1600 soundings were taken, or an average of 129 soundings per 
square mile of surface. The aggregate volume of water contained in 
the lochs is estimated at 14,500 millions of cubic feet, and the area 
draining into them is nearly 240 square miles, or twenty times the 
area of the lochs. 
Notes on the Geology of the Shin Basin. 
By B. N. Peach, ll.d., f.r.s., and J. Horne, ll.d., f.r.s. 
Of the area included in the basin of the Shin, only narrow belts 
along the west, north, and east margins have been mapped by the 
Geological Survey. The greater part of the tract is occupied by 
crystalline schists of the types so largely developed in the counties of 
Sutherland and Ross, to the east of the line of complication which 
stretches southwards from Loch Eriboll by the headwaters of the 
Cassley and the Oykell rivers to Ullapool. The course of the Moine 
thrust — the most easterly of the great Post-Cambrian displacements 
described in the “Notes on the Geology of the Assynt District”* — 
runs south from Gorm Loch Mor by Loch Ailsh to near Loch Craggie, 
thence it curves westwards to Knockan beyond the limits of the Shin 
basin. East of this dislocation, the metamorphic rocks include quartz 
schists, quartz-biotite granulites, garnetiferous muscovite-biotite schists 
and flaggy micaceous gneisses. These are pierced by igneous materials 
(granite and diorite) that cover considerable areas, as near Lairg. 
Along the eastern part of the basin there is a belt of Old Red 
Sandstone strata running in a north-east and south-west direction, its 
western limit being approximately defined by a line drawn from the 
Mound station to a point west of Edderton station. Both the middle 
* See p. 178. 
