Sl'U.MAKIXK Tl NMCLIX<; 237 



lake bottom it was found that the cavity had again increased 

 to a depth of 65 ft, whereupon an additional 600 cu. yds. of 

 clay were dumped into it. 



On account of the water leaking through the brickwork, the 

 only dry place to cut through the brickwork and build in an 

 air-lock was just ahead of the brick bulkhead. This lock was 

 completed Aug. 27, and to avoid encountering the danger of 

 the direct connection with the lake at the end of the drift, it 

 was decided to make another detour to the north. On Aug. 28, 

 therefore, the brick on the north side of the tunnel 12 ft back 

 from the end of the brickwork was cut through under 25 Ibs. 

 air pressure, and work proceeded in good, hard clay. The 

 original air-lock was cut out and a new lock built into this 

 clay about 34 ft. from the last detour, to be used in case of 

 further difficulties. After building the tunnel for about 80 ft. 

 from the detour, the soundings again indicated the approach to 

 gravel and water, and on Oct. 14 the water broke through from 

 the bottom in such volume and with such force that the men 

 ran out, closing every air-lock and the valves of every drain in 

 their haste to escape, until the brick ^bulkhead was reached. 

 It was with great difficulty that the portion of the tunnel up to 

 the last air-lock was recovered and cleaned out. 



It was now recognized that a pressure of from 38 to 40 Ibs. 

 of air would l>e needed to hold this water, and accordingly an- 

 other compressor was added to the plant. With a pressure of 

 3<> llw. the water was driven out and the work again started. 

 At this time also an additional 350 cu. yds. of clay were dumped 

 into the hole in the lake bottom. Altogether, 1,620 cu. yds. 

 <>f clay had been put into this hole. 



Loose gravel and boulders, some of immense size, were now 

 encountered, and the work became exceedingly difficult on 

 aeeoiint of the great escape of air. The interstices between the 

 gravel and boulders were not filled with silt or sand, but con- 

 tained water. Moreover, this material extended upward to the 

 lake liottom, as was shown by the escape of air at the surface of 



