Mr Home on the Geology of the Island of Unst. 277 



Glaciation. — Abundant proofs are to be found in the island 

 of the intense abrasion to which it has been subjected by ice- 

 action. The planed surfaces of the gneissose rocks on the 

 Vallafield range where the covering of peat has been worn 

 away, and exposed them to view, the mammillated slopes of 

 the Heogs, and the numerous roches moutonnees met with in 

 the low lying parts, point to the same conclusion. From the 

 appearance of the roches moutonnees in Haroldswick Bay, it 

 seemed to me that the ice which glaciated Unst must have 

 crossed the island from east to west. Unfortunately stri« 

 are not plentiful, which is easily accounted for in the serpen- 

 tine area, by the rapid disintegration of the rock by the atmo- 

 spheric waste. In the quarries at Hagdale, near Haroldswick, 

 however, about a hundred yards from the public road, I 

 found a capitally striated surface. The ice-markings point 

 8*^ south of west; and from their position with reference to 

 the Heog Hills, it is evident that they must have been pro- 

 duced by some agent acting independently of the isle. Mr 

 C. W. Peach has recorded striae from the same neighbour- 

 hood, running N.N.W. magnetic, which, after deducting 23° 

 for the magnetic variation, is about due east and west. 



Boulder clays, Erratics. — The boulder clays met with in the 

 isle are spread out chiefly over the low grounds in an irregu- 

 lar form, and occasionally they assume the drum- shaped 

 arrangement so characteristic of the low lying districts of the 

 south of Scotland. The deposit consists of a stiff*, gritty clay, 

 charged with smoothed and subangular stones of various 

 sizes, and occasionally measuring three feet across. Sections 

 of this deposit are to be met with along the shore at Balta 

 Sound, in pits between Buness and the Loch of Cliff, along 

 the Baliasta Burn, at Loch Watlea, near Belmont, and along 

 the shores of Uya Sound. My attention was specially 

 directed to the district between Balta Sound and the Valla- 

 field ridge, in order to determine the carry of the stones in the 

 77ioraine profonde. Fortunately the wide difference between 

 the serpentine and the gneissose rocks was of the greatest 

 service in helping to decide the direction of the ice movement. 

 The evidence from this source fully confirmed the conclusions 

 already arrived at, from a consideration of the roches moutonnees 



