MIDDLE AND UPPEE ORDOVICIAN. 203 



[Part of\ synoptical table' of the geological formations about Quebec City, Quebec — Continued. 



The classic descriptions of these Ordovician terranes by Logan ^*^* will be found 

 in his comprehensive monograph of 1863. An interesting discussion of Logan's 

 views on the stratigraphy and structure of this region is given by J. W. Dawson.^^* 

 Selwyn^^^ in 1884 prepared a general description, in which he stated his understand- 

 ing of the stratigraphy and structure of the region. 



The latest comprehensive and detailed account of the Ordovician of the St. 

 Lawrence Valley away from the great cities is by EUs/"*^ as follows : 



The newest rocks of the Cambro-Silurian found in this area are situated to the west of the 

 great St. Lawrence and Champlain fault, between it and the River St. Lawrence. They are 

 evidently the southwestern extension of the Utica-Lorraine beds which occur along the river 

 on both sides between Quebec and Three Rivers. They are well characterized by fossils, which 

 are found at several places and of which very considerable collections have been made, as at 

 St. Hyacinthe and St. Hughes, on the Yamaska River, Chambly Basin, and St. Jean Baptiste 

 village (the latter on the River Des Hurons, which joins the Richelieu a short distance above 

 Mount St. Hilaire), and at Chambly. Rock exposures are, however, rare throughout this entire 

 area. Farther north, on the lower part of the Becancour, opposite Three Rivers, a small col- 

 lection of fossils was made in 1888, which showed the presence of the typical Lorraine shale for- 

 mation at this place and served to indicate the apparently uniform extension of these rocks 

 throughout this area. 



The rocks of the Lorraine formation differ somewhat in character from those of Utica. 

 They are more sandy in texture, and are generally of a grayish color or have frequent beds of 

 gray sandy shales, which sometimes pass into sandstone layers. The Utica, on the other hand, 

 is generally characterized by the presence of brown or brownish-black bituminous shales, with 

 occasional hard bands of dolomitic limestone, but gray beds hke those of the Lorraine are rarely 



seen. 



The valley of the St. Lawrence, from Lake St. Louis almost to Quebec City and for some mUes 

 on either side of the river, is occupied by strata of the Utica and Lorraine formations, between 

 which the line of separation at most points is difficult to ascertain, owing to the great mantle of 

 clay so widely distributed throughout this area. This region was one of the first studied by the 

 Geological Survey. The strata exposed are nearly horizontal, disturbances being few and due 

 to intrusive masses of doleritic matter. The rocks where exposed abound in fossils, and their 

 true horizons can therefore be readily determined. The doleritic rocks which intersect these 

 strata form mountain masses, sometimes of large extent, which present conspicuous features 

 in the otherwise monotonously level landscape. 



