NATURAL HISTORY SOCIETY OF GLASGOW. 153 



ice, and other agencies, have produced gorges. At the places 

 where they appear at the foot of the chfifs, caves are formed, some 

 of but little extent, while others, two especially, penetrate to con- 

 siderable distances. On the west, where the tide divides, and 

 where the abrading action of the waves is at present going on, 

 one cave, called the Water Cave, may be visited at low water. A 

 trap dyke has been worn away, and into tliis the waters rush, 

 wearing down and making further progress day by day; the 

 height of the entrance at high water will be from fifteen to twenty 

 feet. Karely have I enjoyed a prettier sight than once, when 

 pulling round to see the cave at high water, I rowed in between 

 the two cliffs, and there lay in the boat as it heaved up and down 

 on the breast of the sleeping ocean. Around and above me 

 wheeled and screamed thousands of birds, beneath me waved 

 tangles and weeds; but nothing gave me such delight as did two 

 kittiwakes, who had built their nest on a broken column at the 

 entrance to the cave, and there sat in peaceful security, displaying 

 their graceful forms, and lending some living interest to that 

 cave, into which, with long prolonged boomings, the sea dashed. 

 Tliis cave is above the low tide level, and is guarded during low 

 tide by a reef of columns which are slowly wearing away. 



On the opposite side of the jutting headland to the south, 

 another cave of considerable dimensions may be seen. At present 

 the entrance is more than fifty feet above the sea level, but in 

 the interior it is much less, as waste of the cliffs falling from 

 above, and the debris from the trap dyke, has almost filled up the 

 entrance. The trap dyke that has been worn away to form this 

 cave (M'lnall's) is more than twelve feet in breadth, and is joined, 

 a little above the entrance to the cave, by another dyke which is 

 nearly as broad; the column enclosed between these dykes is much 

 changed in its character. On the south face, at what is called 

 the Main Craig, a curious freak of a trap dyke was examined. 

 For a considerable distance from the base of the cliff it keeps on 

 one side — the east — of a column, and then abruptly bends, divid- 

 ing the column, and continues on the other side — viz., the west — 

 as far as the eye can reach. These dykes may be traced the 

 whole leng-th of the Craig from north to south, and make those 

 natural terraces which add so much beauty to the eastern slopes 

 of the island. The path of these dykes is always covered on the 

 hill by immense heaps of stones and abrupt precipices, in some 



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