Clifton Collef/e Scientijic Society. 85 



of the sea, as in the Bays of Norwick, Haroldswick, and Balta. The 

 diallage is hard, good instances of which property are the Islands of 

 Balta and Hunie. 



A few words may be said with regard to the form of hill peculiar 

 to the difierent formations. The serpentine hills of Crucifield, Mica- 

 ford, and Keen, have a smooth, round appearance, without any sharp 

 and rugged peaks. This is due to denudation, weathering, and solu- 

 bility. Heog's Hills, nevertheless, terminate in abrupt peaks, which 

 I think is due to a hard intrusive rock running up through them. 

 The diallage hills are somewhat broken, but the gneiss ridges on the 

 west have a much more rugged outline, and are generally higher than 

 the other hills. Saxaford Hill is an example of a micaceous mass. 

 It is of round shape and terminates on the north and west in a high 

 cliff, into which the sea has bored many caves. 



The numerous brooks of Uust all run pure as crystal, owing to the 

 rocky ground and the absence of mud ; but on the western side of 

 the island, the peat imparts to the small pools a black opaque colour. 

 In some places I observed that the saturated turf, rendered elastic 

 and air-tight by the exuberant moisture, was inflated by the air and 

 water beneath into bubble-like swellings, which sink under the feet if 

 walked on ; if these tumid risings are pierced the water rushes out. 



Climate. — The climate of Unst may be called wet and variable. 

 Thunderstorms ai-e not common, and little snow falls in winter, — the 

 gulf stream keeping the summer and winter temperature from much 

 variation ; the mean annual temperature is only 2^^ lower than that of 

 Edinburgh. The Aurora Borealis is sometimes seen here to great 

 advantage. 



Whatever may be the effects of a damp atmosphere on the human 

 system, it undoubtedly promote healthiness, for the longevity of many 

 of the inhabitants of Unst is remarkable. When I visited the island 

 the Rev. Dr. Ingram was passing his 99th year, and the 71st of his 

 ministry, retaining full intellectual vigour. The resident physician. 

 Dr. Edraonston, though 84 years of age, still carried on active 

 pi-acticc ; and these are by no means solitary instances of the age of 

 its inhabitants. 



I was unable to ascertain the exact amount of rainfall, but it is 

 considerable. A day, however, seldom continues rainy throughout, 

 the showers being short and sudden. 



Geology. — The rocks, now under our notice, may all be classed as 

 metamorphic, and include gneiss, micaceous, talcose and chlorite 

 schists, primitive crystalline limestone, serpentine and diallage, 

 together with hypersthene, hornblende, slate, etc. The accompanying 

 map shews the order of succession. There are many interesting 

 topics here for the chemical geologist to discuss : as to whether the 

 serpentine is a metamorphosed limestone, and the relation of such 

 minerals as chromate of iron, amianthus, and asbestos, to tlieir con- 

 taining rocks. 



The Gneiss occupies the entire length of the western side of the 

 island, from Hermaness to Bellemont, aud, as before mentioned, forms 



