Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/67

SCOTLAND.] GOAL 53 Carboniferous formation, the only exceptions being the little patch of Oolitic coal at Brora in Sutherland and certain thin seams which occur intercalated among the Miocene volcanic rocks of the Western Islands. The Scottish Car boniferous Formation is divisible into four series, viz., 1. Coal Measures; 2. Millstone Grit; 3. Carboniferous Limestone series ; 4. Calciferous Sandstone series. Coal is confined chiefly to the first and third of these groups, but in West Lothian and Mid-Lothian the lowest (calciferous sandstones) yields some coals, one of which has been worked (Houston coal, 6 feet thick). These coals are associated with the well-known " oil-shales," forming a peculiar deve lopment of the upper portion of the calciferous sandstone series which is not repeated elsewhere in Scotland. The millstone grit contains no workable coals. The coal bear ing strata of the coal measures and limestone series are irregularly distributed over the central or lowland district of the country between a line drawn from St Andrews to Ardrossan, and a second line traced parallel to the first from Dunbar to Girvan. Throughout this region the strata are disposed in a series of basins, of which there are properly speaking only three, namely, (1) The basin of Mid-Lothian and Fifeshire, which is bounded on the west by the calciferous sandstone series and some older strata, forming the Peritland hills, Arthur s Seat, the rolling ground that extends west of Edinburgh into Linlithgow- shire, and the heights behind Burntisland in Fifeshire, and in the east by the barren sandstones and igneous rocks of the calciferous sandstone series in the east of Hadding- tonshire and Fifeshire; (2) The basin of Lanarkshire and Stirlingshire, the eastern boundary of which begins in the south at Wilsontown, and runs north by Bathgate and Borrowstounness to the borders of Clackmannan, extends west to the foot of the Campsie and Kilbarchan Hills, and is separated by the Paisley and Dunlop Hills from (3) the basin of Ayrshire, the main mass of which is bounded in the south and east by the valley of the Doon, the Silurian uplands behind Dalmellington and New Cumnock, and the calciferous sandstone and Old Red Sandstone heights which overlook the heads of the Ayr and Irvine valleys. Two small outlying coal-fields lie beyond these boundary lines, viz., the Girvan and Sanquhar (Dumfriesshire) coal fields, but both belong geologically to the Ayrshire basin. Although there are thus only three great basins, it is usual, nevertheless, to speak of five principal coal-fields, each of which is named after the county in which it is roost abundantly developed. Thus we have the coal-fields of Ayrshire, Lanarkshire, Stirlingshire, Fifeshire, and Mid- Lothian. /shire. Ayrshire Coal-fields. The Ayrshire basin, owing to undulations and faultings of the strata, comprises a number of subsidiary coal-fields, such as those of Girvan, Sanquhar (Dumfriesshire), Dalmellington, New Cumnock, Lugar and Muirkirk, Kilmarnock, Kilwinning, Dairy, &c. The coal measures of this basin are of variable thickness ; they contain from 5 to 8 and 11 principal coal-seams, yielding a united thickness of from 13 ft. to 40 ft. The Carboni ferous limestone series of Ayrshire sometimes contains no workable seams of coal, while occasionally its seams eqiial or surpass in number and thickness those of the coal mea sures. Thus in the Girvan field there are 7 coals with an aggregate thickness of 50 feet, while at Muirkirk the same number yield a thickness of 40 feet of workable coal. The Ayrshire coals consist chiefly of common coals, including " hard" or " splint" and " soft" varieties. In some districts the intrusion of igneous rocks has converted certain seams into "blind coal," a kind of anthracite, much used for steam purposes. Gas or parrot coal (so called from its dr.- crepitating or chattering when heated) is met with here aud there, chiefly near New Cumnock. Parrot coal often occurs in thin lines or bands, which, when intercalated aud alternating with dark carbonaceous ironstone and coaly matter, form seams of what is called black-band ironstone. The Ayrshire black-bands occur chiefly at Dairy, Lugar, and Dalmellington. Lanarkshire Coal-fields. These are the most extensive Lanark in Scotland, covering an area of not less than 150 square shire, miles. The coal measures, which attain a thickness of upward of 2000 feet, contain about 18 workable coals; but all these are not continuous throughout the whole coal field, while some are too thin in places to pay the cost of working. At their best they yield an aggregate thickness of 70 feet or thereabout, but in many places they do not average more than 40 or 30 feet, or even less. The lime stone series is well-developed in the Lanarkshire coal-fields, but it is a very variable group, as indeed is the case throughout Scotland. It consists of upper, middle, and lower groups, tho coals being confined chiefly to the middle group, only one or two seams occurring in the lower, while in the upper only one seam occasionally attains a workable thickness. The principal coals of the limestone series vary in number from 1 to 9, their aggregate thick ness seldom reaching more than 15 feet. The Lanarkshire coals consist chiefly of varieties of common coal, namely, hard or splint, soft, dross, &c. But here and there excel lent gas coal is worked, as at Auchenheath, Wilsontown, <fec., the former being considered the finest of all the Scotch gas coals. Another well-known parrot coal is that of Bog head near Bathgate, the subject of much litigation. Par rot or gas coal frequently occurs forming a part of mussel- band and black-band ironstones, which seams, when traced along their crop, are often seen to pass into gas coal. The best known blackbands are those wrought at Palacecraig, Airdrie, and Quarter, Bellside, Calderbraes, Bowhousebay and Braco, Goodockhill and Crofthead, Earnockmuir, Possil, Garscadden, and Johnstone. At Quarrelton, Renfrewshire, an abnormal development of coal seams occurs below the horizon of the main or Hurlet limestone, which is usually the lowest important bed in the limestone series. The strata underlying that limestone contain here and there irregular lenticular patches of coal, never of any value. At Quarrelton, how ever, a number of these seams come together, and form a mass of coal more than 30 feet thick. Stirlingshire Coal-fields. These embrace the coal-fields Stirling of Falkirk, Carron, and Grangemouth, Slamannan, Clack- sllire< mannan, and Borrowstounness. In the Falkirk, Carron, and Grangemouth fields, the coal measures are about 600 feet thick, and contain 9 workable seams of coal, yielding an aggregate thickness of 30 or 31 feet; the thickest seam is only 4 feet. In the Slamannan field, the coal measures are some 720 feet thick, and show G workable coals, yielding an aggregate thickness of 15 or 16 feet, the thickest seam being 4 J feet. A small outlier of coal measures at Coney- park, however, gives a depth of 1140 feet of strata, con taining 12 workable coals (two of which are 7 feet thick re spectively), which yield an aggregate thickness of 44 feet. The coal measures of the Clackmannan district attain a thickness of 900 feet, and yield 10 workable seams of coal (thickest seam 9 feet) with an united thickness of 41 feet. The limestone measures of the Stirlingshire basins contain, as a rule, few coal seams. Where these are best developed, they vary in number from 5 (Bannockburn) to 1 1 seams (Oakley); and their aggregate thickness ranges from ll feet to 37 feet. The coals embrace the variety usually met with in Scotland, viz., hard (or splint) and soft coals, some of the seams being good caking coals. Good gas coal was formerly obtained at Oakley; and other coarse parrot coals occur in various parts of the fields. Oil shale and black-

band ironstone are alsoltnet with. The coal-field of Bor-