274 Proceedings of the Royal Physical Society. 



for the all sufficient reason, that there are not noiu, and never 

 %uere, any rabbits on Heligoland. 



II. On the Geology of the Island of Unst. By John Horne, 

 Esq., F.G.S. (of H.M. Geological Survey of Scotland). 



The island of Unst is the northmost of the group of the 

 Shetland Isles, and measures about twelve miles in length, 

 and about five miles in breadth. It is separated from the 

 adjacent island of Yell by the narrow Blue Mull Sound. 

 The western portion of the island consists of a ridge of high 

 ground called the Vallafield range, running nearly north and 

 south, and more or less parallel with the strike of tlie under- 

 lying rocks; its highest elevation being about 697 feet. As 

 the ridge is followed southwards to Belmont, it sinks in 

 height, and rolls with a gently undulating slope towards the 

 shore. This ridge is planted on the east by a hollow which 

 crosses the island from Burra Fiord to Belmont, in the line 

 of which lie several lochs, viz., the Loch of Cliff, Loch Watlea, 

 and the Belmont Lochs. In the north-eastern portion of the 

 island lies a group of heathery hills, the highest of which is 

 the Saxafiord Hill (938 feet). To the south of this mass, and 

 between Haroldswick Bay and the south end of Loch Cliff, 

 run the Heog Hills, which are upwards of 400 feet in height 

 by aneroid measurement. The ground round Balta Sound, 

 and westwards to Baliasta Kirk, is low lying and cultivated 

 in part, but southwards towards Uya Sound, a distance of 

 four miles, the district is moory, and only a thin covering of 

 turf conceals the underlying rocks. There is a marked con- 

 trast between the physical features of the island between 

 Haroldswick Bay and Uya Sound, and those presented in 

 the more elevated tracts. We shall see presently that this is 

 due to a corresponding difference in the lithological character 

 of the rocks in the respective areas. The coast line round 

 the western and northern portions of the island is rugged, 

 forming in places precipitous cliffs, the most imposing being 

 met with in the neighbourhood of the Flugga lighthouse. 



Geolo(jical Structure. — The Vallafield range, already referred 



