Section IV, 1891. [ 67 ] Trans. Roy. Soc. Canada. 



VI. — On the Geology of the St. Clair Tunnel. 

 By Frank D. Adams, Lecturer iu G-eology, McG-ill University. 



(Communicated by Sir William Dawsou and read, May 27, 1891.) 



The St. Clair Tiiuuel, one of the most useful aud important engineering works of 

 recent years, runs under the St. Clair River from Sarnia, Ontario, to Port Huron, Michigan, 

 and joins the Chicago & Grand Trunk Railway in Michigan with the Great "Western 

 Branch of the Grand Trunk Railway in Canada. These points had formerly been con- 

 nected by a steam car ferry, but owing to the great annual expense and the uncertainty 

 of this means of communication, especially in winter, when the ice from Lake Huron is 

 passing down the St. Clair, as well as to the steady increase of traffic over the line, it was 

 decided to tunnel the river at this point, so that a continuous track might be laid. 



The tunnel proper was commenced in August, 1889, aud finished in August, 1890, 

 the work being thus completed within about one year, the time being the fastest yet 

 made in tunnel construction. 



The work was begun by opening horizontal cuttings to the required depth on either 

 side of the river, and on each of the headings thus formed a tunnel was commenced by 

 means of Beach hydraulic shields, the tunnels finally meeting under the river and thus 

 completing the work. 



The tunnel is 6,000 feet long and 21 feet in diameter, the walls being constructed of 

 cast iron segments bolted together. 



As the tunnel passes through the heavy deposits of drift which cover this portion of 

 the boundary of Canada aud the United States, it seemed probable that an examination of 

 the material excavated might prove of interest. Sir Joseph Hickson kindly consented, on 

 request of Sir William Dawson, to secure specimens of the material passed through as the 

 work proceeded, aud this was arranged for through the kindness of Mr. .Tames Hobson, 

 the chief engineer of the tunnel ; eight samples, taken from different points between the 

 Canadian and American ends of the tunnel, being forwarded to the Peter Redjiath 

 Museum of this University and placed in the hands of the writer for examination. 



General Geology of the District. 



Resting on the Laurentiau axis, whose southern edge forms the eastern shore of the 

 Georgian Bay, 180 miles northeast of Sarnia, there is, as is well known, a regular succes- 

 sion of Palœozoic strata, having a general southwesterly dip aud forming an almost con- 

 tinuous series from the horizon of the Black River beds to that of the Chemung. These 

 underlie what is known as the peninsula portion of the province of Ontario. Passing 

 over the St. Clair River, into the state of Michigan, we find these highest beds succeeded 



