358 Proceedings of the Boy a! Physical Society. 



its present position by the subsidence of the land. There are, 

 indeed, but two other ways by which the peat can be found to 

 form the sea-coast ; one is by the action of the sea upon the 

 shore, the other by the peat advancing to the sea by slip. But 

 neither of these cases will apply to the sea threading in among 

 the knolls and hillocks, eating out holes at first, which become 

 pools, then lagunes, till at last the land that enclosed them is 

 all gone. It must therefore be accepted as a fact, that the 

 land has subsided (and is subsiding) since the peat began to 

 form, and, consequently, that the stone circles of the Lewis are 

 of an age anterior to that subsidence ; it follows, then, that if 

 the rate and quantity of subsidence were known, and supposing 

 it to be uniform, we should arrive at the least age of the Pagan 

 monuments. 



Although we cannot arrive at the whole quantity, we have 

 fortunately a measure of a part of that subsidence ; this is 

 afforded by what have foolishly been called submarine forests, 

 but which are in fact submerged peat-banks. 



In the Orkneys I have noted six places at which submarine 

 peat is said to be found ; at Otterswick, in Sanda, I have seen 

 the people digging it at low water for fuel. The peat was 

 mainly composed of twigs and leaves, and the seeds of the 

 birch were plentifully scattered through it. There were also 

 many gnarled pieces of wood, of the thickness of a man's arm, 

 I was informed, on describing the kind of peat found at Otters- 

 wick, that the same sort of fuel may be got at Balranald, on 

 the west of North Uist, at the level of low water. Peat also 

 occurs below mud and gravel between tidemarks at the head 

 of West Loch, Tarbert, in Harris ; and Martin, the historian 

 of the Hebrides, speaking of Pabbay, an island in the Sound 

 of Harris, says, " The west end of this island, which looks to 

 St Kilda, is called the Wooden Harbour, because the sands, at 

 low water, discover several trees that have formerly grown 

 there. Sir Norman Macleod told me that he had seen a tree 

 cut there, which was afterwards made into a harrow." Se- 

 veral traditions could be added, of places now submerged 

 that were formerly the sites of chapels or houses ; and I think 

 it may be taken as proved, that since the commencement of 

 the peat-forming era, the land has sunk or subsided twelve 



