298 COALFIELDS AND COLLIERIES OF AUSTRALIA. 



At a depth of about 149ft. 8in., a strong blue clay was en- 

 countered , and its resistance was sufficient to prevent the 

 further sinking of the cylinder by the above-mentioned 

 method, so a trepan, or chopper, was devised by the manage- 

 ment made of bar-iron, wood and boiler-plate, and was fitted 

 with four knives at each end, and two in the centre. Figs. 

 192 and 193. This was worked percussively, and cut up the 

 clay so that It could be filled into buckets by the divers. 

 Until this clay was met with, the water rose and fell in the 

 shaft at the same time as the tides. When a diver intended 

 to operate, the water was baled out to a minimum depth over 

 the diver of 60ft., this head of water being necessary to prevent 

 any inrnsh of alluvial while the diver was working on the 

 bottom. The diver worked under water from two to four 

 hours at a time, the period being generally limited by the 

 rising of the water in the shaft to a maximum of 110ft. While 

 operating, the safety chocks were placed under the ends of 

 the weight bearers to prevent any undue or sudden sinking of 

 the cylinder, resulting from the removal of the clay. Too 

 much clay must not be taken out at a time, neither must it 

 be removed from too near the edges of the cylinder until the 

 cylinder has been sunk further down. At 135ft. 6in. the lateral 

 pressure and adhesiveness of the alternating day-beds was so 

 great that it was considered inadvisable to increase the 

 weights, which then amounted to 1400 tons loading, and 

 approximately 102 tons 14cwt. of cylinder, for fear any addi- 

 tional weighting might have seriously fractured the cylinder 

 and caused a collapse of the shaft, so it was decided to reduce 

 the diameter of the shaft by telescoping it. To get an idea: 

 of the strata to be passed through, two boreholes were put 

 down by churn drills. The shaft was then filled to the top 

 with sand, and the work of telescoping commenced. At 

 165ft., a hard agglutinated mass of shingle 7ft. 6in. was met 

 with, which gave trouble, as the size of the stones were very 

 variable, and consequently caused unequal resistance to the 

 downward movement of the cylinder. The inner or tele- 

 scoped portion of the tubbing was sunk from the surface in a 

 similar manner to the outer tubbing. A water-tight connec- 

 tion was made between the inner and outer lining by drilling 

 holes through the cylinders, and running cement through 

 them till it solidified'. 



The winding engine at the Hetton colliery was made by 

 Davidson, of Durham, England, and has two 26in. diameter 

 cylinders and 4ft. 8in. stroke. Besides the ordinary dial 

 depth indicator, there is a knocker indicator, which shows the/ 

 number of knocks that have been given on the face of a dial, 

 so that there shall be no mistake in case the engine driver 

 miscounted the knocks. At the end of the knocker line is- 



