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
Fig. 1.
quicksand and blue clay, twenty-one feet of blue clay of an adhesive and putty-like character and increasing in density, and then the rock. In 1886 a company was organized, and in January, 1889, the work was commenced. After various tests and experiments, necessary from the difficulty of boring 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. They 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.
