56 



west from the CuchuUin group, completing the evidence for the 

 origination of the requisite force within the CuchuUin group itself. 

 Other localities appear to exhibit traces of a great and general wave 

 which has acted parallel to itself over a vast extent of country ; but 

 here no such explanation can apply, and in steep ravines, scarcely 

 half a mile long, we cannot imagine the generation of vast and re- 

 peated waves, or floating icebergs or pent-up lakes, as any of the 

 machinery which has elsewhere been used to account for facts less 

 stubborn than those presented by the adamantine surfaces of the 

 CuchuUin hills. 



2. On the recent Eruption of Hecla, and the Volcanic 

 Shower in Orkney. By Dr Traill. 



Dr Traill read an account of dust faUing from the atmosphere on 

 the 2d and 3d of September last, in the islands of Orkney. 



This dust was observed by a gentleman in the island of Rousay, 

 falling from the air in the morning of the 2d. It was collected by 

 another at SkaiU, on the western shores of Pomona, on the moraing 

 of the 3d ; and by two other gentlemen in Kirkwall on the same 

 day. It appears also to have fallen in several other parts of Orkney, 

 probably over all the islands ; and was observed also to reach the 

 northern coasts of Caithness, within an area of which the radius can- 

 not be less than 30 or 40 miles. 



It covered, to the depth of from j\ to ^ inch, linen laid out to 

 dry, glass frames in gardens, and the leaves of plants of every kind, 

 with a fine brownish-grey dust, almost impalpable to the touch, but 

 meagre and crowding between the teeth. It does not effervesce 

 with acids, and consisted chiefly of silex, alumina, oxide of iron, with 

 a trace of lime. 



This dust bears much resemblance in composition and appearance 

 to that which covered the decks and rigging of vessels in the West 

 Indian seas, when the eruption of the Soufriere took place in St 

 Vincent, in 1812. Those who collected the dust in Orkney, state 

 the probability that it proceeded from some eruption of Hecla, as the 

 ashes of that volcano once before fell in Orkney ; and the wind for 

 several days before the 2d of September had blown strongly from 

 the NW. 



The truth is, that such an occurrence has at least three times be- 

 fore happened in the Ojkney and Zetland Isles, when there has been 



