S42 



MINE. 



Minei of a pit dry is an important point, great attention is paid 



Coal. O t ne d o j n g of it well. When it happens in an engine- 



WUm^nff^ P' 1 tnat taere are a g reat many beds of coal found in 



cual.field. tne shaft, a mine a few yards long is driven into each 



coal, and a bore put down from one coal to another, 



the water is gathered into each coal, and descends 



through the bores to the pit cisterns. 



The practice of keeping the shafts dry, as now de- 

 scribed, is very generally adopted in Great Britain, 

 when the pits are of a moderate depth, and when all 

 the water found in sinking can be drawn by an engine 

 of a moderate power. But in very deep pits, such as 

 those in the counties of Northumberland, Durham, and 

 Cumberland, where they are from 80 to 150 fathoms 

 in depth, the preventing of the water found in sinking, 

 from being a burden upon the engines, is most care- 

 fully attended to, and is one of the chief points in the 

 science of mining. In this operation, much skill and 

 resolute determination are displayed. The mode of 

 passing through the cover, and the various modes for 

 preventing the water from that source descending into 

 the pit, have already been described. The next thing 

 is to point out the plans which have been successfully 

 adopted for preventing the water found in sinking from, 

 flowing into the pit, and becoming a burden upon the 

 engine. Those strata which generally produce the 

 greatest feeders of water, are the sand-stones, particu- 

 larly those of an open porous texture, or those which 

 have very open cutters. Sometimes both these quali- 

 ties are combined, and then the growth of water is un- 

 commonly great. Several of the sand-stones are, how- 

 ever, impervious to water, and almost all the beds of 

 light-coloured argillaceous schistus or fire-clays, are par- 

 ticularly so, being very close in their texture. But 

 some of the sand-stones, though impervious to water in 

 their texture, have wide and open cutters which pro- 

 duce much water. Feeders of water are also frequent- 

 ly found at the beds or partings betwixt two of the 

 strata. Those strata which are impervious to water are 

 said to be capable of turning water. 



While the sinking of one of these deep pits is going 

 forward, a regular journal is kept of every part of the 

 operation, and each feeder of water is measured, not 

 only after it is found, but daily, to find if its growth 

 increases, abates, or is regular. The mode of measur- 

 ing is by receiving the water into a vessel of 30 or 60 

 gallons content, and finding, by a seconds watch, the 

 time required to fill it. Three experiments of this kind 

 are made at each trial, and the average time of the three 

 entered in the journal. When the feeders of water in 

 one or more of the strata sunk through, are producing 

 such a quantity of water, as to render the stopping of it 

 back absolutely necessary, the first thing to consider is, 

 whether any of the strata passed through under the 

 feeders, are impervious, or capable of turning water; 

 and if there are none, the pit must be sunk till a stratum 

 of that kind is found ; then the strata are to be examin- 

 ed upward, until a similar stratum is fixed upon. There 

 are three methods of keeping back the feeders ; viz. by 

 plank tubbing, iron tubbing, or by oak cribs. As the 

 pressure to be resisted is the next consideration, it be- 

 comes necessary to explain its extent or limits. To il- 

 lustrate which, Fig. 14 represents a pit sinking through 

 cccxc. the various strata, having a cover of sand with much 

 Fig. 14. water resting on the rock head. It is evident, from 

 what was explained when treating of the forms of coal- 

 fields, that each stratum sunk through in any pit, whe- 

 ther near the surface, or at the greatest depth, rises in 

 one direction until it meets the alluvial cover ; for 



Feeders of 

 water in 

 the pil 

 chaft. 



which reason, the pressure of water at the bottom of Mines of 

 the tubbing which rests on the rock- head, is as the L 'oal- 

 depth of the water found in the cover ; and if a stratum T~"" * 

 a is found to yield a great quantity of water, and that W 'i'fi"id * 

 the stratum b above, and the stratum c beneath it, are 

 impervious to water, if the porous stratum a is twelve 

 feet thick, and no water found in the strata passed 

 through from the rock head, until that depth which is 

 supposed to be fifty fathoms from the surface of llie wa- 

 ter in the cover, in this case, the tubbing or cribbing 

 has not to resist the pressure of water of twelve feet 

 only, but it must be made of strength sufficient to resist 

 a column of water equal to a perpendicular nltitude of 

 fifty fathoms ; because the stratum a meets the alluvial 

 cover at d, the fountain-head from which all the water 

 found in sinking proceeds. Upon this principle, though 

 no feeder of water was found of any magnitude until 

 the pit had been sunk 100 fathoms, if this water re- 

 quired to be tubbed off in a stratum only three feet in 

 thickness, the tubbing would require a strength equal 

 to the resisting of 100 fathoms of pressure ; for although 

 the water may only come through the open pores of 

 the stone, yet, when the water is resisted, these innu- 

 merable tubes act upon the tubbing with the full effect 

 of the whole hydrostatic column ; for it is found from 

 experience, that whatever water occurs in pits, or in 

 the working of mines, proceeds from the surface. A 

 clear understanding of this principle is an essential 

 point in mining. Upon this principle also, if the cover 

 which rests upon the rock-head is of impervious clay, 

 very little water will be found in the strata ; but if 

 sand beds rest upon it, or rivers run along it, the water 

 will be very abundant. 



From this view of the great pressure of water found 

 in sinking, the tubbing it off is an operation of the first 

 consequence, and requires much skill, attention, and 

 practice. If several fathoms of the strata are to be 

 tubbed, in order to resist the flow of water, the pit has 

 to be widened regularly to admit the kind of tubbing 

 proposed to be put in. The greatest width being 

 required for plank tubbing, and the least width for 

 iron tubbing. Fig. 15. represents a pit widened out p LiTR 

 for plank tubbing, where a, a, a, a, arc the impervious cccxc. 

 strata, b, b, the porous strata yielding the water, the bot- Fife'- '& 

 torn of the recess c, e, is made level, rim! as smooth as 

 possible, by means of mason irons The same points are 

 attended to in working off the upper part of the recess 

 d, d. In this operation, wedging cribs, spiking cribs, 

 and main cribs are used ; besides the plank which forms 

 the tub, a quantity of fine dry clean reeded deal is pre- 

 pared for forming the joints, which is known by the 

 name of sheeting deal. This sheeting deal is> always 

 applied in pieces laid end- ways; that is, with the end- 

 reed of the wood towards the area of the pit. As much 

 of the security depends upon the tub being water-tight 

 at its jointing with the rock, several plans have been 

 adopted for this purpose, the most approved of is repre- 

 sented, Fig. 2, Plate CCCXCI. 



In order to give room for the lower wedging crib, the PUTS 

 recess is cut a few inches wider, as at c, from b to c is cccxci. 

 laid with sheeting deals all around the circle, or with a Fi S- 2 - 

 thin uniform stratum of oakum. Upon this the wedg- 

 ing crib d is laid, and neatly jointed to the radius of the 

 pit, each segment trained exactly to the circle. At 

 each joint of the segment sheeting deal is inserted. 

 This wedging crib is about ten inches in the bed, and 

 six inches deep. The space e, at the back of the crib, 

 about two and a half inches wide, is filled with pieces 

 of clean reeded dry deal, inserted end- ways ; and thi* 



