MINERALS AND GEOLOGY OF CANADA. 7 



great lakes were united into one vast fresh-water sea, held back, on 

 the east, by an elevation of the gneissoid belt of the Upper St. Law- 

 rence or perhaps by a huge glacier-barrier extending in that direction, 

 as explained on a former page. 



7. The St. Lawrence Basin : — This Basin is separated from the 

 Basin of the Lakes, just described, by the gneissoid band, which, 

 passing southwards from the Lac des Chats on the Ottawa, crosses the 

 St. Lawrence at the Thousand Isles, and forms the Adirondack region 

 of New York. On the other hand, it is cut off from the Eastern or 

 Metamorphic Basin (although, strictly considered, this forms an isolated 

 central portion of its area) by the great dislocation alluded to under 

 §5, above. This dislocation, accompanied both by a great upheaval 

 and the manifestation of active metamorphic forces, runs from near 

 the northern extremity of Lake Champlain to Quebec, and from thence 

 along the north shore of the Island of Orleans, and down the river and 

 gulf, as far as the coast of Gaspe, which it enters near the mouth of 

 the Magdalen River. The area of the St. Lawrence Basin thus includes 

 the peninsula between the gneissoid belt, the lower Ottawa, and the 

 Upper St. Lawrence, together with a large extent of the south shore 

 of the latter river, and all the north shore from the Ottawa to the 

 Gulf, except a small portion (including the chief part of Quebec) lying 

 within the above mentioned line of dislocation. It may be considered 

 to include, also, the extreme eastern and southern parts of Gaspe ; the 

 Island of Anticosti, and the Mingan Islands. Towards the western 

 part of this area, more especially in the peninsula just west of the 

 junction of the Ottawa and St. Lawrence Rivers, the Potsdam and Cal- 

 ciferous formations (Map : Nos. .3 and 4) are well displayed, together 

 with the Chazy and Trenton limestone beds (Nos. 5 and 6) . The latter 

 occur also largely on the eastern side of the Ottawa, as around Mon- 

 treal, &c. ; whilst the Utica and Hudson River formations extend 

 more particularly along each bank of the St. Lawrence up to (and on 

 the north, beyond) Quebec — apart from the small area, immediately 

 around Quebec itself, cut off by the before-mentioned dislocation. At 

 the Falls of Montmorenci, the Trenton, Utica, and Hudson River di- 

 visions occur in force ; and the latter runs along the north side of the 

 Island of Orleans. These formations occur also in the small outlying 

 basin of Lake St. John on the Upper Saguenay. The Trenton lime- 

 stones form likewise some isolated patches on the north shore of the 

 Oulf, as at the Seven Islands, the Straits of Belle Isle, &c. ; whilst the 



