GEOLOGY OF THE ST. CLAIR TUNNEL. 69 



lent of the Erie and Saugeen clays laid down under different conditions. This Leda clay 

 will be referred to again later on. 



Character of the Strata penetrated by the Tunnel. 



Judging from the character of the depol^it there is reason to believe that the St. Clair 

 tunnel passes through boulder clay, though being in places very sandy, and having in 

 some places a certain stratification, it pnrtakes of the character of the Erie clay, which, as 

 above mentioned, graduates into the boulder clay, and may really prove to be a peculiar 

 development of it. The material obtained from the tunnel is a stiff clay, in places, as above 

 mentioned, very sandy, and elsewhere very gravelly, while occasionally large gneiss 

 boulders are found embedded in it. 



When dry it is grey in colour, but assumes a pale reddish yellow tint on burning. 

 Judging from the samples received it is entirely destitute of fossils. 



This clay rests on a dark bituminous shale, with abundance of Protosalvinia Huron- 

 etisis, characteristic of the so-called " Huron shale " of Chemung age, vv^hich is well ex- 

 posed in Ontario at Kettle Point on Lake Huron, and is extensively developed on the 

 Michigan peninsula. This Huron shale was struck at the bottom of a shaft which was 

 sunk for drainage purposes close to the Canadian end of the tunnel and, as seen in the 

 accomimnying section, also occurs only a few feet below that portion of the tunnel which 

 is beneath the river bed. 



Two specimens of the rock from the bottom of this shaft were forwarded by Mr. 

 Hobson. One consists of a thinly laminated brownish black bituminous shale holding, 

 as above mentioned, an abundance of Protosalvinia Huronensis} When a fragment of 

 the shale is held in the flame of a Bunsen burner it decrepitates slightly and takes fire, 

 being sufficiently bituminous to continue burning for some time after having been re- 

 moved from the flame. The other specimen is harder and less thinly laminated as well 

 as less bituminous than the one just described. It also contains Protosalvinia. It is, 

 however, highly calcareous, effervescing readily when treated with dilute hydrochloric 

 acid, while the first mentioned specimen does not effervesce at all. The Chemung beds 

 exposed at the bottom of the shaft, therefore, consist of highly bituminous shales inter- 

 stratified with coarser, less bituminous and highly calcareous strata. 



As above mentioned, although some of the samples of drift received consisted of a 

 comparatively pure clay, they generally contained a great deal of gravel or sand. 



The following notes kindly sent me by Mr. Joseph Hobson, chief engineer of the 

 tunnel, will explain their mode of occurrence : — 



" Immediately over the rock there are a number of strata of quicksand and rough 

 gravel. The thickness of these strata A-aries from two to three feet up to six leet. 



"With regard to the sand found in the clay during the progress of the work it was 

 usually in the shape of pockets, although occasionally the beds of clay were separated by 

 films of sand not much thicker than a piece of coarse paper ; in ûict these seams were so 



' Sir William Dawson, 'On Rliizocarps in tlie Brian (Devonian) Period in America" (Bull. Chicago Acad, of 

 Science, Vol. i, 1SS6) ; also " On Sporocarps discovered by Prof. E. Orton in the Erian Shale of Coliimbns, Ohio" 

 (Canadian Record of Science, 1S8S, p. 1.37). 



