A vein may be 30 or 40 ft. thick, and so poor in ore as not to be worth working; again, it may be only a few incites thick, and yet its richness may amply repay the labor of extracting it. Three or four feet may be taken as the average of several kinds of veins. In extensive mines, portions of the ore are here and there left in the lode, so as to furnish a steady supply when other parts are unproductive. These are called eyes, and when they, are afterwards removed, the operation is termed picking out the eyes of the mine.
The old plan of ascending and descending the mines by ladders, so destructive to the health of the miners, is still largely in use. The ladders are now about 25 ft. long, and set with a slope. There is a platform at the bottom of each called a sollar, with a man hole in it leading to the next ladder beneath. Some of the Cornish mines are half a mile deep, so that it takes the miner an hour to reach the surface after he is done with his work; most of the journey being accomplished on wet, slippery ladders. The bad effects of the fatigue so produced are augmented by the fact that the men come from a constant temperature of 80° or 90° F. below, to one of perhaps 30° or 40° on the surface. Dr. J. B. Sanderson states, as the result of recent inquiries, that 90° F. is the highest limit of temperature consistent with healthy labor in a mine.
A great improvement on the ladder system is now in operation in several of the deep Cornish mines. It is a method first introduced into the deep mines of the Harz, and called the fahr-kunst. The plan of this " man-engine " is this. Two rods descend through the depth of the shaft, and upon these bracket-steps are fixed every 12 feet. Tbe rods 11107C up aud down alternately through this distance by means of a reciprocating motion. If the miner wishes to ascend, he places himself on the lower step Of the first rod, and is raised by the first movement of this rod to the level of the second step on the second rod, to which he now crosses. The next movement raises the second rod, and brings the second step up to the level of tin. third step of the first rod, to which he next crosses; and so, ascending stage by stage, he reaches the top. The descent is, of course, accom plished in the same way.
Some of the Cornish pumping-engines are very large and powerful. The cylinder of one of the largest is 7 ft. 6 in. in diameter. With the expenditure of one bushel of coal,
it can raise 100,000,000 lbs. weight one ft. high; this is called its " duty." It lifts nearly SOO gallons of water per minute, and its cost was about £8,000.
In Cornwall the miners are divided into two classes: one of them called tributers, who take a two months' contract of a portion of the lode; the other called tutmen, 'who are employed in sinking shafts, driving levels, etc.
A detailed analysis of one of the largest Cornish copper mines, published some years ago, shows that in that year it produced, in round numbers, 16,000 tons of ore, realizing £90,000, and yielding/a net profit of about £16,000. It employed about 700 miners, 300 laborers, 300 boys, and 300 women and girls. The cost for coal was £1800; for malle able iron and steel, £1300; for foundry castings, £2,000; for ropes, £1000; for candles, £1800; for gunpowder, £2,000; and for timber, nearly £3,000. The last mines regula tion acts were passed in 1872 (amended in 1875). See AATNES ts LAW.
.31ining for Coal.—The minerals of the carboniferous formation, at least those which -occur in beds or strata, as coal and clay ironstone, are mined, as has been already said, in a different way from metallic veins. Originally deposited in a horizontal position, they have been so altered by movements in the earth's crust, that they are rarely found so now. They are more generally found lying in a kind of basin or trough, with many minor undulations and dislocations. But however much twisted out of their original position, the different seams, more or less, preserve their parallelism, a fact of great ser vice to the miner, since beds of shale, or other minerals, of a known distance from a coal scam, are often exposed when the coal itself is not, and so indicate where it may be found The great progress made of late years in the science of geology has made us so minutely acquainted with all the rock formations above and below the coal measures, that it is now a comparatively easy matter to determine whether, in any given spot, coal may or may not be found. Nevertheless, large sums are still occasionally, as they have in past times been very frequently, wasted in the fruitless search for coal, where the character of the rocks indicates formations far removed from coal-bearing strata.