186 
Proceedings of the Royal Society 
I. 
Observations on Boulders and Drift on the Pentland Hills. 
By Alex. Somervail, Stationer, Edinburgh. 
Besides the boulders described by the late Mr Charles Maclaren 
in his “ Geology of Eife and the Lothians,” and also by Professor 
Geikie in the “ Edinburgh Memoir of the Geological Survey,” as 
having been carried from the Highlands, there are others which 
would indicate a transport from a different direction. 
On the highest summits of the Pentland Hills (Scald Law, Car- 
nethy, South Black Hill, North Black Hill, and others which are 
composed of various varieties of porphyrites) are found numerous 
boulders of fine conglomerates, grits, and sandstones, intermingled 
with a few boulders of quartz, greenstone, and other rocks, all par- 
tially or entirely covered by a deposit of peat, which in some places 
on and near the summits of the hills attains a thickness of nearly 
six feet. The sandstone boulders vary in size from mere fragments 
up to large masses which I was unable to dig up. They are common 
on the very highest point of Carnethy (S. 1),* more so on Scald Law 
(the highest of the range) and South Black Hill, and still more 
abundant on the West or North Black Hill. They are smaller in 
size and less numerous as we approach the hills in the neighbour- 
hood of Edinburgh — viz., towards the east. 
On a careful examination of the above-mentioned sandstone 
boulders, with regard to mineral composition, texture, and colour, 
there can be no doubt that they have been derived from the sand- 
stone strata which form the Cairn Hills. The highest point of the 
Cairns is 1844 feet, or 46 feet below the level of Carnethy, and 54 
feet lower than Scald Law, which is 1898 feet above the sea-level. 
It would follow from this, that the transport of the sandstone 
boulders has taken place from S.W. to N.E., or very near this direc- 
tion. There are other indications which confirm this movement. 
Mr John Henderson has, in the “ Transactions of the Edinburgh 
Geological Society,” vol. ii. page 365, described the occurrence of a 
* A plan of a portion of the Pentland Hills, to illustrate Mr Somervail’s and 
Mr Henderson’s notes, is appended. On this plan the localities mentioned 
by Mr Somervail and Mr Henderson are indicated by the letters S. and H. 
respectively. 
