328 Reports and Proceedings. 



within a few miles of the western shore, forming a steep escarp- 

 ment to the west and a long slope to the east, across which the dis- 

 integrated materials of the great mass of these mountains must have 

 been conveyed (probably by floods carrying masses of ice), and 

 deposited in the hollows of Eastern Sutherland. Of the rocks com- 

 posing the mountains, Sir K. Murchison was inclined to regard the 

 micaceous flags and schists overlying the lowest Silurian quartzites 

 as the probable source of the gold found in Sutherland, and he 

 expressed an opinion that no considerable body of rock charged with 

 rich auriferous bands would be discovered in the North Highlands. 



The Eev. J. M. Joass said that the extent of country over which 

 gold has been ascertained to occur in the south-east of Sutherland 

 and contiguous portion of Caithness may be stated as measuring 20 

 miles from north to south, and about thirty from east to west. 



The prevailing rocks of the district, which are flaggy quartzites 

 and micaceous beds dipping S.E., are now ascertained to belong to 

 the Lower Silurian System. 



The associated rocks on the S. and S.E. are, (1) Old Eed Sand- 

 stone, occurring as conglomerate cliff's at Cambusmore, &c., overlain 

 by the argillaceous shales of Sydera with fucoid plants, and the 

 thick-bedded light-coloured Sandstones of Dornoch with Holopty- 

 cJiius : isolated mountain-masses of conglomerate occur throughout 

 the district. (2) Along the coast from Dunrobin to the Ord of 

 Caithness, rocks of Liassic and Oolitic age occur. (3) The igneous 

 rocks associated with these are the porphyritic granite (a) of the 

 Ord, between the Lower Silurian and Devonian rocks, and found to 

 contain purple fluor-spar, — a fine-grained red granite (b) abundant 

 throughout the auriferous district, conforming in its courses to the 

 strike of the flaggy Gneissose strata, — and a friable granitiform rock 

 (c), mostly felspathic, generally associated with the richest auiiferous 

 drifts. 



In the Uisge-dubh and Allt-Smeorail, Strath Brora, gneissose 

 and quartzose beds occur, dipping S. and S.E., associated with con- 

 formable courses of granite (b) and small quartz veins. The over- 

 lying drift is at bottom argillaceous, with boulders of neighbouring 

 rocks passing upward into gravel and sand, apparently arranged by 

 running water. . On the river Helmsdale, above the junction of the 

 Crask and Cill-Donnan roads, micaceous rocks, dipping N.E., are 

 traversed along the strike by granite (b) which sometimes sends out 

 short dykes across the beds, as if into transverse fissures, from which 

 small veins strike off between the strata or lines of least resistance. 

 Here a small trap-dyke crosses both igneous and stratified rocks. 



Two miles to the north of this point, at the head of Suisgill burn, 

 a favourite resort of the diggers, the white granitiform rock (c) 

 appears to cross at right angles highly inclined beds of friable 

 gneissose rock. The detritus of (c) occurs in patches of felspathic 

 clay throughout the drift, and is generally associated with the richest 

 auriferous deposits. The best washes have been found in a similar 

 connection in Cill-Donnan burn, three miles to the S.E., and also 

 near small quartz-veins, thinly encased in chloritic clay and tra- 



