Found by Ian Suddaby at Mugiemoss, Aberdeenshire. This example is not in my possession. Dykehead Firebrick Works, Bonnybridge, Stirlingshire. GR Dykehead – probably stands for General Refractories. (Note – SBH – A similar example found is stamped GR’s. Has the – ‘s – fallen off this stamp or is this a variation on a theme?)….
1920 – Dykehead Ganister and Firebrick Co., Ltd, (Formerly George Turnbull & Co.), Bonnybridge. Dykehead Mine – Situated at Bonnybridge, at the side of the North British Railway, Glasgow to Edinburgh line; it is 1/2 mile east of Greenhill Junction on the Caledonian Railway. Maps: One-inch New Ser. Ordnance and Geological 31; six-inch Stirling 30 N.W. Latitude 55° 59′ 21″. Longitude 3° 52′ 45″. Geological age: Millstone grit. The Dykehead Fireclay Mine is at present (1916) being extended and deepened. Hitherto only fireclay has been worked, but to meet the great demand for silica bricks it is now intended to use the associated ganister seams. A railway siding is being made to the mine at Dykehead; Brickworks are in course of erection, with crushing and mixing mills, drying sheds, and kilns of the continuous Newcastle type. (These are now (1917) in operation At the new works, an output of 500,000 bricks a month is expected. The full section of strata which it is intended to work is not yet completely opened up (Dec 1916), but will average some 24 ft. in thickness, and will be worked in three benches. A section recently examined in the newly-driven road showed: — Sandstone roof Ft.In. 1. Fireclay … … 0 8 2. Coal and blaes 0 4 3. Fireclay 1 6 4. Ganister 3 6 5. Coal 1 2 6. Brown rib 0 3 Coal 0 4 7. Fireclay and Ganister.
- This is a very variable seam and elsewhere in the field reaches a thickness of 3 to 6 ft.
- A 3 to 7-inch dirty coal, apparently very constantly present and a useful local index-mark.
- Also very variable, locally as much as 4 to 5 ft. Both 1 and 3 contain irregular patches and lenticles of ‘ganister.’ Sometimes indeed the ganister predominates and the clay occurs as partings.
- The top foot or so of this seam is somewhat flaky in character, the rest were seen in the new road was an excellent ganister, pale-buff in colour, fine-grained, even-textured, rooty and somewhat micaceous.
- Tyritous coal, averaging about 1 ft. 2 ins.
- Is a brownish irony rib.
- Includes fireclay and ganister proved in borings, but not yet fully exposed in the mine. The combined thickness varies from 12 to 15 ft. and is composed of Fireclay Ganister 2 to 3 ft. (approx.) Fireclay This ganister may occur either near the top or near the centre of the fireclay; it is similar In character to the upper seam. Description of rock. 19581. Top part of the bed. Fine-grained pale-grey, highly micaceous sandstone. Average grain about 0″05 mm. mainly quartz and mica. Cementing material argillaceous, but has locally developed carbonate of iron in small crystals and patches. No secondary silicification. 19582. Lower part of the bed. Pale-grey fine-grained, soft micaceous sandstone, with carbonaceous streaks. Grain angular, about 0*05 to 0*1 mm. Mostly quartz and mica. Interstitial matter argillaceous. No secondary silicification. Reserves: Large. Products: The ganister will be sold in the ground raw condition (both wet and dry); silica-bricks and blocks will be made.