Slates of North-east Scotland
|From: Richey, J.E. and Anderson, J.G.C. 1944. Scottish slates. Wartime pamphlet No. 40. London : Geological Survey of Great Britain.|
Distribution and geological features
In Banfshire and Northern Aberdeenshire a rock-group termed the Macduff Slates forms an outcrop about 8 ml. wide which stretches from the coast at Macduff southwards for 23 ml. to the vicinity of Gartly. Slates, in the strick sense of the word, form only a small proportion of this group which also includes slaty flags, greywackes, fine-grained schistose grits and coarse pebbly grits. In the northern part of the area the ground is comparatively flat and the overburden heavy. The slates are revealed in numerous isolated outcrops, many of which have been quarries. They were also worked on the coast N. of Mill of Melrose, where they split into thin sheets, but were said to be rather soft and crumbling. None of these workings was of any great extent or important and they are not therefore dealt with here in detail.
South of Huntly the slates form a line of hills where they are free from overburden. Here they were formerly worked in a long series of quarries of quarries which extends from west of Gartly eastwards to the Glens of Foudland (for details see below). The slates wrought in these quarries were once widely used in the north-east of Scotland. They are, however, somewhat thick and of a rather dull colour, and it is doubtful if they are every likely to be worked again on any important scale.
To S. of the quarries the slates come against the northern margin of a large mass of igneous rock, the Insch gabbro. Near this intrusion the slates are greatly altered by heat and have lost their cleavage. Further from the igneous rock they have a spotted appearance, but may still possess a good cleavage, as can be seen, for example, in the more southerly quarries in the Hill of Foudland.
Some distance W. of the Macduff Slate Group a belt of flaggy schists, mica-schists, phyllites and slates run from the coast east of Cullen inland in a south-easterly direction past Mulben, W. of Keith, to a point not far from Craigellachie. The slates were formerly worked at Newmill, 1½ ml. N. of Keith, at Melben, 5 ml.W of Keith, and at Tarrymount. The quarry at the last-named locality is the largest and lies on the E. side of the disused Keith-Buckie railway 5¼ ml. N. by W. of Keith and 4½ ml. S. by W. of Buckie. The slates dip E.S.E. to S.E. at 20º, but are not now well exposed, as the quarry face is much obscured. They were said to be of only moderate quality, and it is doubtful if they would be work considering as a subject for future exploitation.
Some 3 ml. E. of Dufftown there is a belt of black graphitic schists which belong to a geological horizon different from that of the Tarrymount rocks. These black schists were also wrought at one time for slates, although they are not believed to have been of good quality. One of the quarries lies 1,150 yds. E.S.E. of the ruins of Auchindown Castle, which is 2¼ ml. S.E. of Dufftown, and the other on the N.E. slopes of the Hill of Machalea, 3¼ ml. E. by S. of Dufftown.
Considerably further S. than the exposures just described there is a band of fine-grained micaceous slaty flagstone which runs in a north-easterly direction some 2½ to 3 m. N.W. and N. of Tomintoul. This rock, which may belong to the same geological horizon as that of Tarrymount, has been worked for many years, and up till quite recently, at Cnocfergan Quarry, on the W. side of the River Avon, 2¾ ml. N.W. of Tomintoul. As well as slabs for building and paving purposes, it is understood that roofing slates were also produced.
Gartly to Glens of Foudland
Six inches to the mile; Aberdeen, Sheets 34 S.W., S.E.; 35 N.W., S.W., N.E.
|Locality||The Macduff Slates were formerly worked in a long line of quarries stretching from the Hill of Kirkney, 5 ml. S. by W. of Huntly to the Hill of Tillymorgan, 8½ ml. E.S.E. of Huntly. All these openings have been abandoned for a long period.|
|Access||The more westerly quarries on the Hill of Kirkney and the Hill of Corskie are close to the main road S. of Huntly and to the L.N.E. railway at Gartly station. The more easterly quarries can be reached from the main road which runs south-eastwards from Huntly through the Glens of Foudland, or from branches of the same road.|
|Description of slate||Colour dark blue-grey, banding not common. Surface even, somewhat rough; texture rather coarse. Pyrites very rare. Small flakes of mica seen on cleavage surfaces. Slates appear to be fairly thick.|
|Dips, with amounts||Cleavage-dip S. 10º E. at from 30º to nearly 90º. Bedding-dip often coincident with that of cleavage, but sometimes slightly oblique.|
|Joints||The slates are traversed by numerous, fairly widely spaces, joints, which follow a variety of directions, none of which appears to be dominant.|
Details of workings
The most westerly quarries are those on the N. face of the Hill of Kirkney, W. of Gartly station, which form a long of openings over half a mile long. The furtherest W. of these openings is about 350 yds. long and 30 ft. deep. For the most part a band of slate-rock some 30 ft. wide has been worked; at the W. end the quarry face extends southwards, but whether it penetrates another band or the same band displaced by a fault is not clear. Small holes occur to E., and then another large opening about 100 yds. long and some 30 ft. wide. Overburden at these quarries is absent, but at their upper edges the slates show an abnormally low dip and are much broken owing to surface creep.
On the opposite side of the valley, E. of Gartly station, there is another line of quarries nearly half a mile long on the N.W. face of the Hill of Corskie. There are several small holes to W. 20 to 30 ft. deep, followed by a large opening to E. about 200 yds. long and 30 ft. deep, which appears to have been worked in a band some 20 ft. wide. The most westerly quarries are offset to N. from the line of this band but whether a fault intervenes or whether they have been opened in a different seam is not clear. There is no overburden, but surface creep has occurred.
About a mile E. by N. of the workings just described occur the Haining Quarries and a little further to the eastwards the Roughouster Quarries. These consist of a number of small openings which need not be described in detail.
A further 2 ml. E. by N. there are a number of openings in the Wishach Hill, which lies W. of a road branching southwards from the main road 4 ml. S.E. of Huntly. There are about half-a-dozen small holes, clearly very old and now largely obscured by debris and vegetation. These openings are from 10 to 20 ft. deep and appear to have been worked in bands 10 to 20 ft. thick. From the position of the holes, two main belts seem to have been wrought. Overburden is absent.
To E., on the opposite side of the road, great numbers of small holes occur on the W. side and around the top of the Hill of Foudland. The most extensive workings of the whole area, however, are the Foudland Quarries on the N. side of the hill, S. of the main road which runs south-westwards from Huntly through the Glens of Foudland. The workings are now much obscured, owing to debris, surface creep and vegetation. To W. the openings are in some cases of considerable size and include one about 200 yds. long, although the depth does not exceed 30 ft. Two main seams, about 200 yds. apart, appear to have been worked. Farther E. there are a number of smaller openings. In the Foudland Quarries the slates are sometimes spotted, due to heating by an intrusion of igneous rock, the Insch gabbro, the northern margin of which lies 1½ ml. to the S. The spotting therefore comes on in this direction, although it does not appear uniformly at first, but in certain bands. At the quarries it is only slightly developed, and does not seem to interfere with the cleavage.
Brief mention may be made of small openings on the Hill of Skates, E. of the Foudland Quarries. Still further to the E. by N. beyond the main road, there are other old workings in the hill of Tillymorgan. These mark the limit of the series of quarries, as farther to the E. the ground falls and the slate-rock is covered with overburden.
At all the localities described above ample reserves occur, both laterally and in depth. In most cases it would probably not be easy to reopen existing quarries, as the faces are in bad condition owing to surface creep and to debris. It might, therefore, be more advisable to make new openings nearby on the line of the seams as revealed by the positions of the old workings. At the Foudland Quarries in particular the ground is so broken by old workings and covered with debris that the opening up of new ground slightly to the W. would probably be necessary.
Future exploitation is not likely, but if it should take place, perhaps the ground on either side of the main road at Gartly would be more favourable. Immediately W. of the quarries on the Hill of Kirkney there is a rushy hollow, but beyond the hollow an opening in the hillside ought to meet the workable seam once more. There should also be reserves lower down the hill on the E. side. In the Hill of Corkskie, E. of Gartley, there should also be workable reserves immediately E. of the existing openings.
- Hinxman, L.W. and Wilson, J.S.G. 1902. The Geology of Lower Strathspey. (Sheet 85). Mem.Geol.Surv. (Slate quarries, p. 75-76).
- Read, H.H. 1923. The Geology of the Country round Banff, Huntly and Turriff (Sheets 86 and 96). Mem.Geol.Surv. (Slate quarries, pp. 215-216).
- Hinxman, L.W. 1896. Explanation of Sheet 75 (West Aberdeenshire, Banffshire, Parts of Elgin and Inverness). Mem.Geol.Surv. (Slates, p. 341).