Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/75

MINING. 1 COAL Cl On the west coast of South America, Cretaceous coals are worked at Lota, iu Chili, and at Sandy Point, in the Straits of Magellan. In Peru both Secondary and Carboni ferous coals are known at various points in the interior, the former occupying a position on the first rise of the table land of the Andes, while the latter occur in higher ground, at a greater distance from the coast. Good coal is also found at many points in the Santa valley. Much of the Peruvian coal has undergone considerable disturbance and metamorphism subsequent to its deposi tion. At Porton, 45 miles east of Truxillo, a ridge of coal-bearing sandstones has been changed into a hard quartzite, with an interstratified seam of anthracite in a nearly vertical position. The coal is remarkable as con taining a large amount of sulphur (see analysis Table I.). The hitherto inaccessible position of these places, which are usually more than 10,000 feet above the sea-level, has prevented the development of coal-mining in Peru ; but the extension of railways into the mountains will probably bring them into importance, by stimulating a local demand for fuel. Extent of existing Workable Coal. The following summary of the amount of coal estimated as workable remaining in the different districts, which is taken from the report of the Royal Commission on coal, and founded upon investigations made in the years 18G6-71, furnishes an approximate measure of the comparative value, present and prospective, of the different coal-fields of the United Kingdom. The quantities represent the probable aggregate yield of all seams above 1 foot thick. Coal-Fields. Within 4000 feet. Tons. Coal remaining in exposed Coal-fields. Below 4000 feet. Tons. 32,456,208,913 4,109,987,004 265,000,000 4,218,970,762 1,885,340,220 South Wales, Forest of Dean, Somersetshire, South Staffordshire, Shropshire, f Forest of Wy re f Clee Hills, ) Leicestershire Warwickshire, North Wales, Anglesea, North Staffordshire, Yorkshire and Derbyshire, Yorkshire (Oolitic, &c.) ... Lancashire and Cheshire, . Northumberland and Durham, Cumberland, Scotland, do (Oolitic), Ireland, 1,906,119,768 836,798,734 458,652,714 2,005,000,000 5,000,000 3,825,488,105 18,172,071,433 70,000,000 5,546,000,000 10,036,660,236 405,203,792 9,839,965,930 3,500,000 155,600,000 1,000,785,488 234,728,010 90,000,000 90,206,240,387 7,320,840,722 The quantity estimated as lying above the workable limit of 4000 feet under the Permian and other formations, in the central and northern counties of England, is 56,248,000,000 tons, covering an area of 2044 square miles, in addition to which, in the flat ground between the Mersey, Denbigh shire, the North Staffordshire hills, Cannock Chase, and Colebrookdule, a further area of 843 square miles at inac cessible depths is computed to contain Between 4000 and 6000 feet, 29,341,649,067 tons. 6000 ,, 10000 15,302,741,333 ,, 41,144,300,400 , Adding to this the amount below 4000 feet from the previous table, 7,320,840,722 ,, Total unavailable coal, 48,465,141,122 ,, As compared with 146,454,240,387 ,, the quantity of workable coal, as made up of the two amounts, 90,200,240,387 and 56,248,000,000 tons, given above. From this it follows that, out of the probable total quantity of coal in the P>ritish coal measures, rather more than three-fourths may become available for consumption, or about 1170 times the amount of the present annual out put of 125 million tons. Similar estimates have been formed for the coal-fields of other countries, especially in France and Germany, but it is doubtful whether the necessary structural details are sufficiently well known to admit of more than a tolerably rough guess being made. COAL-MINING. The opening and laying out, or, as it is generally called, Prelimin- " winning," of new collieries is rarely undertaken without a ary trial preliminary examination of the character of the strata by coal-work means of borings, either for the purpose of determining ings the number and nature of the coal-seams in new ground, or the position of the particular seam or seams which it is proposed to work in extensions of known coal-fields. A/.3 N.4 The principle of proving a mineral field by boring is illustrated by figure 3, which represents a line direct from the dip to the rise of the field, the inclination of the strata being one in eight. No. 1 bore is commenced at the dip, and reaches a seam of coal A, at 40 fathoms ; at this depth it is considered proper to remove nearer to the outcrop, so that lower strata may be bored into at a less depth, and a second bore is commenced. To find the position of No. 2, so as to form a continuous section, it is necessary to reckon the inclination of the strata, which is 1 in 8 : and as bore No. 1 was 40 fathoms in depth, we multiply the depth by the rate of inclination, 40 x 8 = 320 fathoms, which gives the point at which the coal seam A should reach the surface. But there is generally a certain depth of alluvial cover which requires to be deducted, and which we call 3 fathoms, then (40 - 3 = 37) x 8 = 296 fathoms ; or say 286 fathoms is the distance that the second bore should be placed to the rise of the first, so as to have for certain the seam of coal A in clear connection with the seam of coal B. In bove No. 3, where the seam B, according to the same system of arrangement, should have been found at or near the surface, another seam C is proved at a considerable depth, differing in character and thickness from either of the preceding. This derangement being carefully noted, another bore to the outcrop on the same principle is put down for the purpose of proving the seam C ; the nature of the strata at first is found to agree with the latter part of that bored through in No. 3, but immediately on crossing the dislocation seen in the figure it is changed, and the deeper seam D is found. The evidence therefore of these bores (3 and 4) indicates some material derangement, which is then proved by other bores, either towards the dip or the outcrop, according to the judgment of the borer, so as to ascertain the best position for sinking pits. The methods of boring are similar to those adopted for Methods of

deep wells, or in other departments of mining. For shal- boring.