Welsh Journals

THE NATURAL RESOURCES OF WALES; VI-SANDROCKS FOR FURNACE BUILDING IN his "Sylva, or a discourse of Forest Trees" (1670) John Evelyn deplored the fact that "Nature hath thought fit to produce this wast- ing ore (that is, of iron) more plentifully in wood- lands than in other ground, and to enrich our for- ests to their own destruction," and it was indeed the case that the iron ores used by our early iron- masters mostly occurred in association with clay- ey rocks that yielded soils favourable to the growth of trees. When, as the forests were cut down and timber became scarce, the ironmasters were compelled to turn their attention to coal as a possible fuel, there was a similar association of fuel and ore, because the kind of iron ore then in use in this country was found almost entirely in the rocks among which the coal seams occurred. This association played an important part in the localisation of the iron-making industry and in the economic development of the country in gen- eral. It was the abundance of wood that first at- tracted the ironmasters to the country between Pontypool and Merthyr where iron ore was abun. dant and easily obtained, and when the hills be- came denuded of their timber, it was the abun- dance of coal in the same region that caused them to remain there it was the necessity for trans- porting the iron that first led to the development of canals and railway transport in South Wales, and the necessity for exporting it led to the rise of Newport, for owing to the geographical configur- ation of the country a town at the mouth of the Ebbw and the Usk was the natural outlet for much of the north eastern region of the coalfield. Although as far as Wales is concerned the iron ore that occurs in the coal bearing strata is now very little used, and ores of other kinds are im- ported from regions outside the coalfields or from other countries, the territorial association of use- ful commodities is still a matter of considerable interest, because many of the materials needed in the construction of furnaces and for facilitating the smelting of the ore, occur in or adjacent to the coalfields. Limestone for assisting in the removal of the earthy material of the ore by forming with it a liquid slag, dolomite for lining the hearths of furnaces to fulfil a similar purpose, and fireclay for use in situations where heat resisting materi- als are needed-all these occur in the rocks of the Carboniferous System, which is also the reposi- tory of the coals of this country and which covers considerable areas in North Wales and South Wales. The foregoing have already been dis- cussed in previous papers in the Welsh Outlook* 1 "Natural Resources of Wales," Welsh Outlook, February, April, June, September (1928). by F. J. North, D.Sc., F.G.S. but another material, equally important, also oc- curs among or in close proximity to the coal bear- ing strata. That material is silica. Although one of the commonest of the constituents of the earth's crust, silica is probably known by name to few people beyond those who have studied the origin and composition of rocks, or are concerned in their exploitattion and commercial use. It occurs in many forms, one of the best known being mineral quartz, grains of which are the principal constitu- ent of most sands and sandstones. Flint, agate and opal, are other materials of which silica is the chief or only ingredient. The forms of silica that are used in connection with iron and steel furnaces are known as silica-rock and ganister. The term silica-rock usually connotes a very pure sand- stone, although the name also includes rocks con- sisting of quartz fragments large enough to be called pebbles (quartz-conglomerate), while ganis- ter is the name given to very fine-grained hard siliceous rocks of granular texture and smooth splintery fracture. The rock originally called gan- ister occurs in the lower part of the coal-bearing strata of the Sheffield district, but the name has now been applied to similar, but not always identi- cal, rocks in other places. Real ganister, like fire- clay, often occurs as part of the seat-earth of a coal seam, and may pass by gradual change into a fireclay rich in silica, but ganister is not of necessity accompanied by a coal seam, although its presence suggests the existence of conditions that would have resulted in the formation of a seam had the carbonaceous material been pre- served. The reason for the importance of silica-rock and ganister is that, like fireclay, they are com- paratively infusible, and so are suitable for use in furnace construction. The rocks are usually broken into lumps of convenient size, crushed, and then ground, but the ground silica rock or ganister differs from fireclay in that it cannot be made into bricks without the addition of some- thing to assist in binding the particles together; the material added is usually lime, in the propor- tion of from one to two per cent., although ex- periments have been made with other substances such as talc, water-glass, magnesia, and china clay. The bricks, when moulded, are dusted with sand or sawdust to prevent them sticking, and are laid on a "drying floor" heated by means of special stoves. After drying for a period varying from 12 to 4.9 hours they are "fired" in kilns (usu- ally those shaped like a bee hive) for about a week, at a temperature in the neighbourhood of 15000 Centigrade; the average number of bricks in a kiln is 50,000.