On Traces of Glacial Drift. 



387 



cently bared rock at the Mill Cove, on the island of Housay, 

 from which I removed more of the drifted clay and stones, 

 and found ruts, strise, and polishing in abundance, and as 

 fresh as if only just done. On the highest point of this 

 island I also found deep ruts and scratches, which had not 

 been obliterated from the hard gneiss. All these scratches 

 run nearly east and west, this being the direction of the 

 channel of the two principal entrances to the harbour, by 

 which Gruna is separated from Bruray. 



The cliff on the north side of the Mill Cove of Housay is 

 about 100 feet high, and nearly vertical. The sea, in heavy 

 gales, breaks on its top, and tears up the rock, and as well 

 throws up material from the deep. So great is the force, 

 that large blocks are driven far back from the edge of the 

 cliff, and piled up into a semicircular-like wall. Between 

 this wall and the cliff a deep river-like gully is scooped out, 

 down which the water thrown up rushes again to the sea. 



The water left in the hollows of tbis gully is brackish ; in 

 it Enteromorpha grows. Mr Jeffreys and myself gathered 

 portions of limpets, mussels, periwinkles, rock-whelks, and 

 other sea-shells, amongst the sand and gravel, both in and 

 on the edge of this gully. 



A portion of the top of this cliff is higher than the gully, 

 and now beyond the influence of the sea; it is also strewn 

 with proofs of similar action, when in all probability the 

 cliff was not raised so high out of the water. Eidges of 

 stones lie all over the hill, and hang on its rounded sides. 

 The whole of the loose blocks and stones rest on rounded 

 knolls and polished rock, all so polished — evidently by 

 glacial drift — before the burthen was thrown there. This 

 is not the only point on which the terrific seas of this wild 

 spot have left traces of the kind ; they are almost on every 

 part, some of the most astonishing and recent are to be seen 

 on the Bound Skerry, an isolated mass of rock on which the 

 splendid lighthouse stands. Mr Stevenson, C.E.,has had many 

 of the stones marked, and the changes watched and noted. 

 Those desirous of farther information will do well to con- 

 sult a paper by that gentleman, printed in the " Proceedings 



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