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steel roof, built up of plates 3 ft long and 1 ft. wide, of J-in. 

 sheet steel, to the four sides of which were riveted angle bars 

 2 x 2 x ^ in. These plates were bolted together in a heading 

 about 6 ft. high. In the erection of this roof, poling-boards 

 were used for each plate, and a bulkhead carried down with 

 each ring as erected. When the heading had been advanced 

 about 20 ft. from the rock, a 12 x 12 in. yellow-pine mudsill 

 was introduced along the bottom of the heading, and on this 

 the roof was covered by means of radial timber bracing. The 

 excavation was now carried down on both sides of tins mudsill, 

 to a distance of about 10 ft from the rock, the steel roof being 

 extended well down on the sides. A circular section was thus 

 excavated, in which brickwork was laid, four courses thick, and 

 with an internal diameter of 10 ft. Between March 4 and 6 

 a great deal of trouble was experienced. Air pressure was 

 several times to 4S Ibs., and the work progressed very slowly 

 on account of the many inrushes of water and softened mate- 

 rial. It was not until April H that the last section of brickwork 

 in the soft material was completed and rock again entered, after 

 passing through 20 ft. of this decomposed material. Of the 

 material met in driving through this vein, at first ft. of the 

 gray decomposed feldspar was penetrated, a vein of 4 ins. of 

 hard quart/ was then met. and this was followed by > ft. of pure 

 white decomposed feldspar, smooth and soft as plaster. The 

 remaining 14 ft. was made up of layers of feldspar and chlorite. 

 This chlorite, deep green in color, flaky and grease-like to the 

 touch when wet, proved to l>e very troublesome material, as it 

 WM easily converted into a fluid state by the water, which was 

 again encountered next to the rock. 



At the Long Island shaft, the work up to this time had pro- 

 LMv-^rd to about 250 ft from the shaft. The material so far 

 encountered on this side was a hard, seamy gneiss, bearing con- 

 siderable quantities of salty water, containing iron, lime, and 

 magnesia. Soft ground was now met at this end, in a seam 

 about 4 ft. wide, of chlorite. As this material was perfectly 



