464 



THE POPULAR SCIENCE MONTHLY. 



low the towns of Sarnia and Port Huron. Though not so narrow 

 as where the cars were ferried, the nature of the bed of the river 

 seemed to be more favorable at that point. Borings were made 

 to the rock, eighty-six feet below the level of the river. The 

 greatest depth of water was 40"47 feet. The bed of the stream 

 was found to consist of the following layers : two feet of common 

 yellow sand like that of the seashore, twelve feet of a mixture of 



quicksand and blue 



clay, twenty-one feet 

 of blue clay of an ad- 

 hesive and putty-like 

 character and increas- 

 ing in density, and 

 then the rock. In 1886 

 a company was organ- 

 ized, and in January, 

 1889, the work was 

 commenced. After va- 

 rious tests and experi- 

 ments, necessary from 

 the difficulty of bor- 

 ing through quicksand 

 and clay under water, 

 and near rock full of 

 fissures from which 

 natural gas escapes, 

 two great excavating 

 shields were started, 

 one on each side of the 

 river. Two cuttings 

 were made, one on the 

 Canada side fifty-eight 

 feet deep, and one on 

 the United States side 

 fifty-three feet deep, 

 into which the shields 

 were lowered ready to 

 begin their work. The 

 shield on the United 

 States side commenced on the 11th of July, that on the Canada 

 side on the 21st of September. Thej^ met on the 30th of August, 

 1890, after traveling six thousand feet. The work had proceeded 

 day and night, by the aid of the electric light, three gangs of men 

 having been employed, in shifts of eight hours. Each shield 

 averaged ten feet per day, and the most accomplished in any one 

 day was twenty-seven feet and ten inches. 





