Mr Home on the Geology of the Island of Unst. 275 



to, consists of diliereiit varieties of gneissose rocks, the strike 

 of the beds varying from 10° to 30° to the east of north and 

 west of south. Tliis persistent strike has determined the 

 direction of the ridge of high ground. The same relation 

 between the trend of the ridge-shaped hills and the strike of 

 the strata is observable in the island of Yell, and also in the 

 Mainland; the escarpments of the ridges facing tlie east, 

 while the gentler slope is inclined to the west. The gneissose 

 rocks are admirably seen in the sea-cliffs and in the streams 

 draining the Vallafield range. The common variety is 

 micaceous-gneiss, consisting of quartz, felspar, and mica ; 

 the felspar being very abundant. The mica is sometimes 

 replaced by hornblende to such an extent, that the rock 

 may be more fitly termed hornblendic-gneiss. These meta- 

 morphic rocks are intersected with numerous veins of granite 

 and pink orthoclase felspar and quartz. Along the eastern 

 slope of the range the beds dip from 10° to 20° to the south 

 of east, but in many places westerly dips j)revail. 



The group of hills round Saxafiord, of which the latter hill is 

 the highest elevation, is composed of different materials. They 

 are mostly round dome-shaped masses, with a comparatively 

 smooth contour, and possessing a tolerably thick covering of 

 peat. The rocks consist of thin flaggy micaceous and talcose 

 schists, the strike of the beds being identical with that of the 

 gneissose rocks to the west, viz., from 10° to 20° to the east 

 of north, while the dip is mostly from 10° to 20° to the south 

 of east. 



Bands of limestone occur at the south-western margin of 

 these schistose rocks along the line of the Loch of Cliff, while 

 other calcareous bands are noted by Dr Hibbert as occurring 

 at the south-west point of Unst, and in the island of Linga. 



The long hollow which extends from Belmont northwards 

 by Loch Watlea to the Loch of Cliff, is approximately the 

 western boundary line between the gneissose rocks of Valla- 

 field and the great mass of serpentine of Heog and Gallow 

 Hills. From thence the line sweeps in a north-easterly 

 direction round the nortliern margin of the Heog Hills to the 

 Norwich Bay. This rock is admirably seen on the Heog 

 Hills, wliere it is exposed on the top and flanks of the ridge, 



