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-l, 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 or 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 denned by a line drawn from the 

 Mound station to a point west of Edderton station. Both the middle 



See p. 178. 



