SflJMAKlNK Tl NNKUNG 239 



some cases of caisson disease be excepted, the only mishap oc- 

 curring was a fire which got into the timber packing behind 

 the lining and caused some trouble. From the gravel the tunnel 

 ran into clay and quicksand, and then into hard, dry clay 

 similar to that encountered near the shore. Some difficulty 

 was had with the quicksand, but it was successfully overcome ; 

 and when tin- hard clay was struck, the trouble, as far as the 

 work from the shore shaft was concerned, was virtually over. 



Meanwhile, a different set of afflictions had come upon the 

 engineer and contractors in sinking the lake shaft and driving 

 the heading toward shore. This shaft was intended to be 

 built by sinking a cast-iron cylinder 10 ft in diameter, made 

 up of sections bolted together. Work was begun July 5, 1892, 

 and the sinking was accomplished first by weighting the cylinder, 

 and afterwards by pumping out the sand and water within it 

 until the pressure from the outside broke through under the 

 cutting edge and forced the sand into the cylinder, allowing it 

 to sink a little. From 10 to 80 cu. yds. of sand were carried 

 into the cylinder each time, and finally it was feared that if 

 the process continued, the crib, which had been previously 

 erected, would be undermined. On Sept. 6, therefore, the 

 contractors were ordered to discontinue this method of work. 

 No change was made, however, until Oct. 1, when the cylinder 

 had reached a depth of 68 ft., and by this time there was quite 

 a large cavity underneath the crib. This was refilled, and the 

 cylinder pumped out, and excavation begun inside of it. On 

 Oct. 11 a 2^-ft deep ring of brick work was laid underneath 

 the cutting edge ; but in trying to put in another ring beneath 

 the first, two days later, the sand and water broke through the 

 bottom, driving the men out, and filling the cylinder to a depth 

 of 16 ft. with sand. The pumps were started, but the water 

 could not be lowered to a greater depth than 60 ft. 



At the request of the contractors, the city engineer had a 

 boring made at the center of the shaft to determine the 

 character of the material to be further penetrated. This 



