On the Coalfield of Brora, Sutherlandshire
Authors: Payne William 
Published: December 2013

A seam of coal is being worked at Brora at a depth of from 270 feet to 300 feet from the surface. It is about 3 feet 6 inches thick. It forms the upper part of the lower Oolite, and dips S.E. of 1 in 4—a dip which forms a serious difficulty in the process of mining. There are several seams of coal at Brora, but the one referred to is the largest, and, indeed, it is considered the largest Oolitic coal seam in Britain. I may remark that the Oolitic rocks of Brora, consisting of limestones, shales, coals, ironstone, and fire-clay, are similar to, and on the same geological horizon as, the lower Oolites of Yorkshire, which embrace the limestones, shales, coal, and ironstone of Scarborough, Gristhorpe, &c., and the workable coal of the Peak, Stainton Dale, and Haiburn Wyke.

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There has been much speculation as to the extent of this field. An opinion has been expressed that there are at Brora at least 350,000 tons of coal yet untouched. It must be admitted, however, that a very different opinion is entertained by several men whose fitness to judge I would not be disposed to question. On the N.W. the coal is shut off by the Silurian rocks; on the E. and S.E. coast near Brora it rises to the surface, and is seen at low water, and, as I have said, it dips rapidly to the S.E. It is thus, apparently, limited on every side. There is a question, however, as to whether the seam seen at low water is the same as that which is being worked in the mine. If it is, there must be a great fold in the strata, or a great fault between the mine and the reef, for at the 1 in 4 dip the Brora seam would be 1600 feet below the level of the reef. On the other hand, we must not exclude the idea that the reef may be part of an overlying seam which has disappeared. In addition to this, I must state that there are evidences, both in the pit and in the rocks above, of violent disturbances and great contortions. Another fact is, that the coal in the reef is inferior in quality to that in the mine, whilst the latter improves the nearer it is to the shore.

The coal hitherto found is not of a superior quality, as may be seen from the following analysis:—

The roof-bed of the main seam consists of 5 feet of impure limestone, which forms the lower part of the middle Oolite, and it abounds in marine fossils. This roof-bed contains as much as 92 per cent. of the carbonate of lime. Above this stratum are strata of fine clay, with hard limestone bands, which are crowded with ammonites and other finely developed specimens.

The shales on which the coal-bed lies are more or less bituminous or carbonaceous. These shales are about 7 feet deep. There are several thin seams of coal and of clay in them. The oils obtained from these shales, although of no great value for light, are found to be valuable for fuel, and will be useful for smelting. There is a 6-inch seam of shale immediately below the main coal-bed capable of yielding 60 gallons of oil per ton; but so poor are the other seams that the average yield of oil cannot be more than 10 gallons per ton. A similar remark applies to the lower seams of coal. In thickness also they are of no great account, being only 6-inch, 7-inch, and 16-inch respectively. At the same time, in presence of what has just been demonstrated at the Seafield Patent Fuel Works, near Bathgate, in the way of converting refuse or waste products into valuable fuel by improved machinery, I do not see why these thin seams of coal and shale may not be regarded as valuable raw materials yet to be employed in the manufacture of artificial fuel. The importance of this idea is enhanced by the fact, that immediately below this shale there is a seam of fire-clay over 30 feet thick, with a band of ironstone from 6 to 9 inches thick, running through it.

The ironstone found at Brora has yielded—

The following is a general section of the Brora coal-field from the surface downwards:—

Of true ‶coal measures″ there are none in the Highlands, there being really no carboniferous deposits north of the Grampians. There are, however, many coal seams in the Oolitic system, of which Brora furnishes examples. Coal has also been met with in Ross-shire, in Nairnshire, in the mainland of Inverness-shire, as well as in Skye. Quite close to Inverness, coal was spoken of many years ago as having been seen on the surface—since covered over. On the historic farm of Leanach a seam of coal 6 inches thick crops up, and, on the same estate, that of Culloden, there are indications of fire-clay. In Strathnairn coal has recently been found; whilst in quite another direction—at Inveraray, in the county of Argyll—a large hole is still to be seen out of which the people used to dig a kind of shale which they burnt along with peats.

It is thus abundantly established that coal is not confined to the areas usually assigned to it, and that this most important field of inquiry is still far from being exhausted.