468 THE POPULAR SCIENCE MONTHLY. 



The difficulties caused by the reef have been at last overcome 

 without having first to remove the accumulation of material by the 

 adoption of a system of shafts and tunnels which is called, after its in- 

 ventor, " Jones's system." A shaft was sunk through the fallen reef 

 within the mine by letting down a scries of caissons till the solid " blue 

 ground " was reached. A hundred feet of loose reef was thus pene- 

 trated, after which the shaft could be extended to any desired depth 

 in the " blue," and tunnels driven in all directions, so as to continue 

 the excavation of the mine underground. The scheme had the merit 

 of entailing little initial outlay, while, as soon as the " blue " was 

 reached, the work of opening up the galleries more than paid for itself 

 in the value of the ground removed. Other shafts have been sunk 

 outside of the mine, one being more than five hundred and twenty 

 feet deep, and others going down to the hard rock, and connected by 

 tunnels and cross-tunnels, so built that the cross-tunnels have a wall 

 of hard rock on one side, while the roof and other side are solid " blue." 

 The excavation, says the report, " is then continued by cutting down 

 the 'blue' from the roof overhead ; but instead of trucking away the 

 ' blue' as it falls, the rails in the tunnel are taken up and the 'blue' is 

 allowed to pack underfoot, the miners therefore being continually 

 climbing to a higher level, while the height of the tunnel remains 

 uniform, just enough for the miners to be 'in touch' wdth the roof." 

 In order to preserve safe means of access and egress for the workers 

 in this continually rising chamber, a couple of cross -headings are 

 driven parallel with it, five feet high by four wide, branching out at 

 right angles from either side of the main tunnel, and leaving a solid 

 wall of "blue " ten feet thick between the cross-headings and the main 

 chamber. " A number of inclined passes are then driven at a sharp 

 angle through this wall of blue, connecting the cross-heading with the 

 working-chamber, and where they strike the latter vertical 'pass-pits' 

 are carried up, rising simultaneously with the chamber, and separated 

 from it by a three-inch plank, which prevents the loose pack of blue 

 from filling the passes. At last the overhead excavation has pro- 

 ceeded so far as nearly to strike the fallen reef which at present covers 

 all the open workings in the mine. The crown of the chamber is then 

 bi-oken through at either end, and the loose reef allowed to enter and 

 pack on the top of the excavated blue. A sliding-door in the planks 

 at the bottom of the pass-pits is then opened and the excavated blue 

 drawn off, sliding down the inclined passes into trucks in the cross- 

 headings, which convey it through the main tunnel and shaft to the 

 surface. As the blue is drawn off, the loose reef above it subsides and 

 takes its place till the chamber is entirely emptied of blue and filled 

 with reef. The sliding-doors are then closed, and the excavation of 

 that chamber is complete." This process is repeated, with modifica- 

 tions in the several chambers as they ar£ successively excavated ; while 

 in another part of the mine an opposite system of excavation is sue- 



