The chief difficulty or obstacle which has occurred in executing day-levels, is thick beds of quicksand which are found in the alluvial cover. Instances have been found in practice where ingenuity, determination, and I esolute perseverance, could not command success ; for although thick beds of quicksand can now be passed through in a perpendicular direction, by adopting ap proved of plans, the difficulty of passing through them in a horizontal line has not yet been surmounted. If such a sand-bed is found to obstruct the driving of a day level ; and if it is an object to carry forward the level from that particular point, the mode of proceeding is as follows. Fig. 8. represents the strata of a coal-field A, with the alluvial cover a, b, containing the bed of quick sand b. B is the lower part from which the level is required to be caaried in the direction B, d. But the quicksand renders this mode of operation impracticable. The pit BC is sunk through the quicksand by means of tubbing, as will be described when treating of pit sinking ; and when the pit has been sunk a few yards into the rock, the level mine or drift is carried forward to the point D, when the pit ED is put down, it having been previously ascertained, by boring through the al luvial cover, that the rock-head at F is a few yards higher than the mouth of the pit B. During this operation all the water and mine stuff are drawn at the pit B ; but the instant the pit ED communicates with the mine, the water is allowed to fill the mine CD, and grow up both pits until it finds an issue at the mound) of the pit B. From the surface of the water at G, in the pit ED, a mine is begun of the common dimensions, and carried forward until the coal in search of is intersected. By this plan no level is lost. This kind of level is named a drowned level, a blind level, and also an inverted syphon. When a coal, or any number of coals, are inter sected by a day-level, the operation of working the coal proceeds in the usual manner, as will be described when treating of the manner of working coal.
In carrying forward levels into a coal-field of such dimensions as to be used as a canal, the same general rules are observed as in driving a common-level, the only difference being in the dimensions ; but, from the width being great, a greater proportion of the sides and root requires to be built and arched for security, w hick greatly adds to the expence of the operation. When such under-ground canals or levels extend to a great distance, they can be easily ventilated without air pits, on account of their width ; or, if ventilation is ne cessary, it is accomplished either by air-pipes, or by wide bore-holes put down from the surface ; so that if air-pits are found necessary, they are placed at a great distance from each other, and as the stuff produced in driving the mine is in great quantity. it is brought to the mouth of the mine by canal-boats; but rail-roads must be used at the forehead. This part of the opera tion is not commenced until the level has advanced about half-a-mile under cover. This mode of proceeding is
represented Fig. 8. Plate CCCXCI V. where A is the canal which elite! s under cover at B, the stuff from which is taken out by means of railroads as far as the point C ; at this place a step is left a few inches higher ill in the depth of the water, and the canal is filled. From the level of this step the mine is carried to the forehead 1), and all the stuff produced is brought in carriages along a ail•road, and emptied into the boats at C. When this operation has advanced to a eut distance, the rail-roads arc lifted, and the step at C is formed with a platform C, a, having an inclined plane formed of the rock a, b, which reaches to the bottom of the mine. The sole is then cart ied forward in a true water level line in the direction b, c, until it is as far ad vanced as the forehead 1). The stuff produced by this last part or the operation is carried along rail-roads ; mid the loaded carriages are drawn up the inclined plane a, b, by means or a jack-roll, or windlass, placed at a, where they are emptied into the boats at C. The next operation is to remove or cut out the step or bench of rock left at C. For which purpose, a temporary dam-head, made of deals, is placed across the canal at C, as high as the water, having clay at the back to pre vent leakage ; the step a, C, is then cut out as low as the bottom of the canal, and upon removing the temporary dam, the water tills the canal to the forehead 1), to which point the boats navigate ; and the same operation goes on successively to any required distance, viz. until all the coals or other minerals of the district, proposed to be laid dry, and wrought by the mine or level, are inter sected.
When a coal-field is so situated as not to be rendered level free, the winning has to be made by means of ma chinery.
In the early periods of mining, the drawing of water from the mines was most laborious, when either men or horses had to be employed ; and when this was the case, the mining operations were very limited, both as to depth and extent below ground. The chain and bucket en gine was the most powerful of the machinery then em ployed, and when wrought with a water wheel, raised a great quantity of water ; but the greatest depth to which it was applied, was from 40 to 50 fathoms. The ma chines or engines presently in use for the drainage of coal-mines are.
1st, The hydraulic engine, or water wheel, with cranks and vibrating beams.
2d, The common atmospheric steam-engine, invent ed by Newcomen, known by the name of Newcomen's engine.
3d, The steam-engine invented by the justly cele brated Watt of Glasgow.
4th, The high-pressure steam-engine, invented by Travethic.
As the principles of hydraulic and steam-engines, with their general application, are treated of under the articles HYDRAULICS and STEAM-ENGINE, these heads are referred to for minute information; and therefore we shall only give a very short account of the engines used in the draining of coal mines, making such practi cal remarks as have arisen from seeing them applied to work.