CHAPTER II. SEARCH FOR COAL. In Untried Districts by the Application of Geological Knowledge-Search in both an Unknown and Proved Coal-field by Boring-The Operation of Hand-boring by the Use of Rigid Rods--Boring with the Diamond Drill-Particulars of Deep Bore-holes-Application of the Result obtained by a Series of Bores-Search for Coal in South Staffordshire-Search for Coal in Kent. THE search for coal in an altogether unknown district is putting the geologist's knowledge to a practical test. He carefully examines the district, making use of roadsides, quarries, cliffs, protruding rocks, the beds of streams, railway cuttings (if any), and ploughed fields. He may by these means be able to ascertain whether the rocks are carboniferous, and if so he must pursue his investigations further. An actual outcrop of a coal seam may be discovered, or the dark appearance of the soil over a freshly ploughed field may indicate the proximity of one, in which case he would remove the soil at places most likely to prove the existence or otherwise of coal, and having found it, he would probably drive a heading into it to prove its dip for some little distance, the direction and amount of which would be noted. But should he have proved the rocks to be unquestionably carboniferous (and the fossils should be an infallible guide to him) his failure by a personal examination to find coal will by no means be conclusive, and he will have to resort to boring. Sometimes, too, the coal measures are covered by the secondary or tertiary rocks, beneath a comparatively thin covering of which the coal measures may be found. Even in a district where coal has been proved and worked, it is often necessary to bore, as before deciding on the site for a shaft it is of importance to know the direction and amount of dip, the nature of the rocks to be sunk through, and the quality and number of the seams to be won. The outcrop of a seam, it must be remembered, affords but little indication of the quality of the coal, as it is much deteriorated from being exposed to atmospheric influences. A personal survey having met with encouragement, boring should be resorted to so that the depth and thickness of the seam or seams, and their inclination, may be ascertained to guide the sinking of shafts to win the coal. The operation of boring may be classified under two distinct heads. The first proceeds by means of a suspended tool, to which is given a percussive motion by either hand or steam-power, and also a rotary motion either by the apparatus itself or by the attendant, the latter motion taking place between each fall of the tool. The second consists in giving motion to a rotating tool which is hollow in the form of a tube, as in a drill used by a Diamond Boring Co. The ordinary process of hand-boring consists first in erecting the headgear, Fig. 4, over the bore-hole for the purpose of supporting the tackle by which the bore-rods are drawn out of or lowered into the hole, when it is necessary to clean out the hole or change the cutting chisel. The headgear may be made of three good, sound Norway spars 8 or 10 inches in diameter, 40 feet high, and formed as a triangle; or four legs may be used with cross pieces; a pair of blocks are hung from the top, or they may be further multiplied according to the depth of the hole. A rope is passed through the blocks, one end of which is attached to a winch and the other hangs loose over the end of the bore-hole. The windlass should be 12 inches in diameter and be fitted with a pawl and brake, so as to regulate the speed with which the rods are lowered. The following are the tools used as described by Greenwell in his Mine Engineering : The ORDINARY BORE-RODS, Fig. 5, 1 inch square, made of best wrought iron 6 or 9 feet long with a male screw at one end and a female screw at the other. LENGTHENERS are from 4 to 30 inches long, and of the same section as ordinary rods. CHISELS, see Fig. 6, are 18 inches long and from 2 to 2 inches in breadth on the face, which is of the best steel; they weigh about 41⁄2 lbs. The WIMBLE, Fig. 7, is 3 feet long, the lower 2 feet being cylindrical, the bottom being partly covered for the purpose of retaining the core in the instrument. It is made of wrought iron of a size suitable" to follow" the chisel. There is an opening a little up one side of it to admit of the loosened material entering it. The wimble is also used for boring through clay. The SLUDGER is also 3 feet long and somewhat resembles the wimble; the lower cylindrical part has no opening in it, but the bottom has a clack for the purpose of retaining borings of a soft nature. The BÊCHE, Fig. 8, is rod in case of fracture. up. The diameter of the used for the purpose of extracting broken pieces of and hollow for about 16 in. in., tapering up to in. In case of the rods breaking, the part above the fracture is withdrawn, the bêche being screwed on to take the place of the broken rod. It is then lowered sharply on to the broken rods in the hole, the force causing them to enter the tapering cavity of the bêche, which grips them whilst they are drawn up. ROUNDERS, Fig. 9, have the appearance of the bêche, but are solid and well steeled at the bottom. They are used for breaking off any irregularity in the holes. The BRACEHEAD, Fig. 10, is a piece of oak or ash 3 feet long and 3 inches in diameter in the centre tapering slightly towards either end, and this is passed through an eye formed in a piece of iron screwed on to the top rod. A man stands at each side to lift the rods and turn them partly round in the hole. For greater depths than 10 fathoms a double bracehead is used. It consists of two similar pieces of wood passed through two eyes in the iron at right angles to each other. Four men stand one at each arm of the double bracehead, to lift and turn the rods, and thus a depth of 20 fathoms is attained. Fig. 10.-BRACEHEAD A BRAKE, Fig. 11, is used below a depth of 20 fathoms. This is simply a lever of Memel fir 10 or 12 feet long, the fulcrum being 18 inches or 2 feet from one end. At its extremity is placed an iron crook, a rope being attached to it and to the bracehead. Two or more men at the other extremity press down the brake and so raise the rods, another man then turns the bracehead partly round, and the men at the brake let it go suddenly, causing the chisel to cut into the ground. When it is desired to take the rods out, the bracehead is unscrewed and a runner, Fig. 12 (A), is attached to the rope which fits on to the topit, Fig. 12 (B), which is then screwed on to take the place of the bracehead. The windlass is used for drawing up the rods as far as the shear-legs will allow, when a key, Fig. 12 (c), is passed under the bottom joint above the bore-hole, and this key holds them in position whilst another key is used for unscrewing them. Another topit is screwed on the remaining portion of the rods, and by means of the runner another portion lifted by the windlass. The process is continued till all the rods are drawn out. Fig. 13 shows a group of improved boring tools, as manufactured by Messrs. Thornewill & Warham, of Burton-on-Trent, and supplied by them singly or in sets. Fig. 13.-MESSRS. THORNEWILL AND WARHAM'S IMPROVED BORING TOOLS. List of Boring Tools in Fig. 13. 1. Shoe-nose shell with valve for bringing up loose stuff. 2. Wrought-iron screwed well bore pipes. 3. Auger for clay and stiff soil. 4 and 5. V-nose chisels for hard ground. 6. Shell-auger with valve for loose and wet soil. 7. Bell-shell with valve for loose gravel. 8. Lifting dog for raising rods. 9. Pair of rod-wrenches for screwing and unscrewing rods. 10. Levers for turning rods. 11. Spring dart for drawing pipes in bore-holes, 12. Bell-box for bringing up broken bits. 13. Spiral worm for extracting broken rods. 16. S-nose chisel for hard strata. 17. T-nose chisel for hard strata. 18. Rods with screw joints in 5 and 10-foot lengths. 1. Shoe-nose shell with valve for bringing up loose stuff. After the cutting tool has been worked for some time the loosened material interferes with its further action, and so it is withdrawn from the bore-hole, and changed for the shoe-nose shell which is then lowered into the hole. Its pointed end is designed to assist its descent. When lowered as far as possible, it is turned round, the rotary motion causing it to descend further as the eroded material passes upward through the valve which afterwards keeps it in place during the ascent. 2. Wrought-iron screwed well bore-pipes. These are used where from the nature of the ground the bore-hole would otherwise partially or wholly close, and are generally made in 10-foot lengths. The first pipe is well steeled and sharpened and very carefully driven or pressed down until its head is nearly level with the ground. By means of pipe-clamps another length is then screwed to the first, the whole being afterwards driven down another length. More pipes are added until the bottom of the hole is reached. Much care is needed to keep the pipes perpendicular. Where a hole is lined with pipes the diameter has of course to be reduced on continuing the boring below them, and if a number of such sets have to be inserted allowance must be made beforehand for the necessary successive reductions of the bore-hole. If this is ignored, it may become necessary on reaching some soft running bed, to enlarge the hole from the surface to admit of the lining. If the boring is to be carried to a great depth, it is almost certain that lining will be requisite. 3. Auger for clay and stiff soil. This tool is used in the same way as an ordinary auger. The clay passes into the interior of the tool and is there withdrawn as a core without the aid of a valve. 4 and 5. V-nose chisels for hard ground. These are shaped so that in coming into contact with the material to be cut the best effect is obtained; they are more suitable for hard rock, and better stand the frequent sharpening required, than the square-nose chisel 15 which, however, is used in all moderately firm ground. In some very hard strata the S-nose chisel 16 and the T-nose 17 are found to cut better. 6. Shell-auger with valve for loose and wet soil. This is used where no cutting tool is required and where 1 and 3 are also unsuitable. After being lowered in the bore-hole till it touches the loosened material the tool is turned round in the same way as I and 3. It is made longer than 3, being the same length as I with a valve which retains the material in the act of withdrawing it. If the valve fits tightly it effectually prevents the return of the pasty, or liquid material which the tool is specially intended for, unless it becomes clogged by grit so as to prevent the proper closing of the valve. As the valve wears some leakage may be expected, it therefore requires attention, as indeed do all valves, springs, and working parts during the continuance of the boring. 7. The Bell-shell with valve for loose gravel is used in the same way as 1, 3 and 6, the tool being square on the bottom and shaped so as to pass through the gravel, which is afterwards retained in the interior by means of the valve until reaching the surface when it is taken out for examination. 8. Lifting dog for raising rods. The rope is secured to the ring of a dog; the lower portion of the dog is then passed under but clear of the shoulder formed at the head of the top rod 18. The portion of the dog which receives the rod is made of a size which allows of the bore-rod passing into it, yet, being less than the shoulder of the rod it comes into contact with the projection on being raised sufficiently. By means of the windlass and rope the rods are raised as far as the head gear will allow. Another lifting dog is then placed on the ground under the nearest rod-joint, the whole length of rods being lowered a few inches till the shoulder at the joint enters the lifting dog, which then takes the weight of the rods, being itself supported by the ground around the bore-hole, while the pair of rod-wrenches 9 are used to unscrew the rods. The unscrewed length is placed in a suitable position for easy re-attachment when required, after which the rope is lowered by the windlass, disconnected from the lifting dog last used, and |