430 BATH YMETRICAL SURVEY OF 



NOTES ON THE GEOLOGY OF THE NORTH-EAST PART OF THE NESS BASIN. 

 By B. N. PEACH, LL.D., F.R.S., and JOHN HORNE, LL.D., F.R.S. 



Only a small portion of the Ness area has been mapped by the 

 Geological Survey. It is situated in the north-east part of the basin, 

 and includes the tract at the mouth of Loch Ness and on either side of 

 the river issuing from that loch. It comprises a small part of Loch 

 Ness, Loch Dochfour, Loch Ashie, Loch Abban, and Loch Laide. 



The geological structure of the northern part of the Ness basin is 

 well denned. The basin is traversed by the great fault that runs along 

 Loch Ness, which is continued north-eastwards to Tarbat Ness, thus 

 giving rise to the prominent cliff bounding the Moray firth in the 

 Black isle. This powerful dislocation, which has been a line of weakness 

 in the earth's crust at successive geological periods and is evidently 

 related to the earthquake movements that periodically affect the Inver- 

 ness district at the present time, has a marked downthrow to the 

 south-east. The exact position of the line of fault in the Ness valley 

 is concealed by superficial deposits, but its course probably extends 

 from near the western shore of Loch Ness at Lochend, north-east by 

 Loch Dochfour, Duneaii cottage, and Kinmylies, to the Beauly firth 

 east of Kessock ferry. 



The effect of this great dislocation in the Ness valley is to let down 

 the Old Red Sandstone strata on the south-east side against the 

 crystalline schists and gneisses of Dochfour hill, the Abriachan granite, 

 and the basal conglomerates and sandstones of Duueaii hill and 

 Craig Leach on the north-west. The schistose rocks of Dochfour hill, 

 which are pierced by the Abriachan granite, consist of quartz-biotite 

 granulites and felspathic gneisses traversed by numerous veins of 

 pegmatite. Occasional lenticles of garnetiferous hornblende-schist 

 are associated with the gneisses, and a band of limestone also 

 occurs in the schistose series at Blairnahenachrie, west-north-west of 

 Dochgarroch. From their lithological characters, these crystalline 

 schists have been referred to the Moine series of the Geological Survey, 

 the members of which are regarded as altered representatives of 

 sedimentary deposits. 



The triangular area of Old Red Sandstone on the west side of the 

 valley of the Ness, extending from Dochgarroch north-east to Clachna- 

 harry, and west to the Bunchrew burn, consists of coarse conglomerates 

 and grits that dip to the north-west, and are overlain by sandstones, 

 flags, and shales. Along their western margin they are bounded by a 

 fault, with a downthrow to the east, which is probably a branch of the 

 great dislocation running along Loch Ness. 



