358 Proceedings of the Royal 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 
