On the Pagan Monuments of the Outer Hebrides. 357 



of these can be approached on foot at low water, and the rest 

 are only separated by shallow channels. On going round the 

 coast I began to notice that the peat banks formed frequently 

 the sea-margin at high water ; and feeling that it was a point 

 of some geological importance, I noted the places on my sketch 

 of the coast, till at last finding that the phenomenon was ex- 

 tremely common, occurring perhaps twenty times in a day's 

 walk, it was no longer necessary to record its occurrence. 

 After examining hundreds of examples, I came to the conclu- 

 sion that, in these instances, there was no other way of 

 accounting for peat banks having that position with regard to 

 the sea-margin, than by the subsidence of the land. In many 

 of the cases referred to, the peat rests at once upon the naked 

 gneiss. Now, the surface of the gneiss is as rugged as, and 

 not very unlike what, the surface of the ocean would be if it 

 were suddenly solidified in the middle of a violent storm. The 

 peat has grown over the undulatory surface, but, as was to be 

 expected, is deepest in the depressions, where I have sometimes 

 seen it in section more than ten feet in height. Let it be sup- 

 posed that the relative levels of land and sea remained the same 

 until the formation of peat had occurred, and then that the 

 land began to subside. The effect would be that when the sea 

 reached the foot of the peat banks small cliffs would form, 

 identical in their features with those of clay or gravel, or any 

 other soft material. But from the extreme softness of the peat 

 the sea would quickly eat it away, and work itself into all the 

 sinuosities of the surface gneiss that were below the level of 

 high water. This is what has happened around Benbecula ; 

 the sea at high water flowing in amongst the knolls, at first 

 forming a simple gap, then branching out like the arms of a 

 tree ; at a further stage in the destruction of the peat, a group 

 of islands is formed, till at last the whole vegetable soil is 

 washed away, and a few bare rocks serve to point out where but 

 one generation ago the cattle have pastured and corn has 

 grown. Some of these rocks, which are now completely bare, 

 still bear the names of particular plants that once grew upon 

 them. It is difficult in words to convey an idea of the 

 appearances and of the facts ; but an inspection of the coast 

 would show that the peat could only have been brought into 



