Seil slate quarries, Easdale slate belt, Scotland

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From: Richey, J.E. and Anderson, J.G.C. 1944. Scottish slates. Wartime pamphlet No. 40. London : Geological Survey of Great Britain.

Balvicar Quarries, Island of Seil[edit]

Sketch map of Balvicar slate quarries. P519821.
Map of Easdale slate belt with inset map showing outcrops near Oban. P519820.

Maps[edit]

Sheet 36 Kilmartin. 1:50,000 geological map

Six inches to the mile: Argyll, Sheet 121 S.E.

Locality E. side of Seil Sound, 1½ ml. E. by S. of Easdale.
Access Quay on Seil Sound ¼ ml. From working quarries; 14 ml. by road to Oban.
Description of slate Colour, bluish-grey, occasionally banded (‘ribboned’); surface, even and smooth, with subdues though definite ‘grain’ (lineation); fairly fine texture; pyrites crystals (‘diamonds’) ubiquitous, numerous, small (less than 1/16 inch in diameter).
Dips, with amounts Cleavage-dip, E.S.E. at 25º to 45º. Bedding-dip, E. 10º S. at 12º to 65º.
Joints A master set of dip-joints is developed, and many others less constant and less regularly disposed also occur.

Details of workings[edit]

The belt of slate quarries extends along a prominent scarp facing W.N.W. and running from a point about 170 yds. S. of the quay on Seil Sound for some 550 yds. in a S.S.W. direction to a point a few yards N. of a farm-road to Winterton. The farm-road connects with the main Oban road at the junction of the Easdale and Cuan branches. The scarp overlooks flat ground to W.N.W. which is an old raised-beach platform. The flat ground is covered by peat, etc. overlying a thin deposit of sand and gravel. The quarries have been opened up along the scarp and on the flat ground adjoining. Along the scarp the slate-rock has been worked to the cleavage-dip, but on the flat ground the quarry faces no doubt were driven to the rise. There are said to be many beds of good slate-rock available.

Some notes concerning the various quarries are appended:

Quarry No. 1[edit]

The original quarry, now worked out. To judge from the area of the level, ‘made’ ground W.N.W. of the main quarry-face, the quarry was very extensive. A quarry-hole filled with water extends around part of the face. The quarry-floor is said to have been taken to a depth of 200 ft. below the level of the water.

Quarry No. 2[edit]

Abandoned, now filled with water. The quarry was sunk to a depth of 200 ft. below the level of the water. Working was stopped to S.S.W. at a W.N.W. inclined whinstone dyke. A cutting has been driven from the S. corner of the quarry through slate-rock traversed by W.N.W. whinstone dykes and therefore useless, and connects by Deccaville track quarry No. 1 (used for dumping ‘waste’) with quarry No. 3.

Quarries Nos. 3 and 4[edit]

Development of these two quarries, which are clear of debris, is at an early stage, and, except for some overburden of peat and sand, their expansion does not appear to entail any geological difficulties. Except for one observation of a reversal in the dip of the bedding at the W.N.W. face of quarry No. 3, the bedding-dips follow closely the direction of cleavage-dip, though differing in angle of dip. The horizon of the slate-rock is the same as that worked in quarry No. 2. A thin inclined sheet of pale whinstone, the ‘white band’ of the quarrymen (P519821) , is apparently a reliable mark for the centre of the slate belt quarried. It follows the cleavage-planes and was found traversing quarry No. 2; it is exposed along the E. side of quarry No. 3.

Quarry No. 5[edit]

The pale whinstone is exposed along the E. side of this small quarry (P519821) , and hare again would appear to mark the horizon of the exploited slate belt.

Reserves[edit]

The unexploited area of slate-rock immediately in prospect lies to the extension of quarried Nos. 3 and 4, especially up-dip across the flat ground to W., as far as a ditch-drain along a fence (P519821) , and also farther to S.S.W. along the scarp and on the adjoining flat as far as the farm-road and quarry No. 5. The reserves are thus very great.

As in other districts, the slate-rock on the flat ground where it is covered by sand and gravel, or directly by peat, is much less weathered superficially than it is along the exposed slate-scarp. It does not appear likely that the amount of overburden along the flat ground will exceed 8 ft., and it may locally be very much less or even practically absent, as in the case of quarry No. 5.

Bren Phort Quarry, Island of Seil[edit]

(P519820)

Maps[edit]

Sheet 36 Kilmartin. 1:50,000 geological map

Six inches to the mile: Argyll, Sheet 121 S.E.

Locality W. side of Seil adjacent to coast, 250 yds, S.E. of the Manse (W. by N. of Kilbride), and 5/6 ml. E.S.E. of Easdale village (Ellanbeich).
Access By side-road passing the Manse 350 yds. from the main Oban-Easdale road, thence 15 ml. By road to Oban. Pier at Easdale, 1 1/8 ml. by road.
Description of slate Colour, bluish-grey, occasionally banded (‘ribboned’); surface, even and slightly rough, with well-marked grain (lineation); texture, fine to medium, pyrites crystals (‘diamonds’) fairly sparse, medium size (1/8 – 3/16 inch in diameter).
Dips, with amounts Cleavage-dip, E. 30º S. and 55º. Bedding-dips, at quarry-entrance, N.W. at 30º, along W. face and in recess at N.W. end of quarry, E. 30º S. at 30º.
Joints A master set of dip-joints is developed, and many others less constant and less regularly disposed also occur.

Details of working[edit]

The workings quarry is a relatively narrow and elongate excavation, extending for about 60 yds. or so along the strike of the leavage (N. 30º E), with walls about 50 ft. in height, the entrance being at the S.W. end adjacent to the side-road. The quarry has been opened in the cliff of the raised beach.

Overburden at the far end of the quarry, from where a grassy hollow extends to the N.E., consists of about 4 ft, of thin peat over gravelly clay. Elsewhere there is practically no superficial overburden, but on the south-eastern (inland) side of the quarry the slate-rock is weathered to a depth of some 6 to 10 ft. The ground on this side rises steeply. Bad top slate is not thick on the N.W. face.

Reserves[edit]

In addition to reserves remaining within reach of the present quarry, the apparently most easily worked reserves lie a short way farther inland. Here, to N.E. of the continuation inland of the side-road, the ground falls abruptly in a scarp facing S.E. and extending from the side-road for a considerable distance to N.E. The cleavage dips approximately parallel with the surface of the scarp, so that a quarry opened up along the scarp would be worked up-dip as it was driven into the scarp. As there is little or no superficial overburden, some considerable amount of weathered slate might have to be stripped from the scarp in the first instance. Quarrying could presumably also be extended in depth at least to the level of the floor of the present quarry. The latter quarry, if abandoned, might be used for disposing of ‘waste’ slate. The locality, at any rate, would appear worth detailed investigation, should reserves be desired in this district.