57 



in general belong to one sub-group including members of 

 Cambrian and perhaps early Ordovician age. 



The strata in the immediate vicinity of Riviere du Loup 

 have never been described in detail. Logan [4, p. 259] 

 merely states that between the coast at Riviere du Loup 

 and Temiscouta lake, "a distance of about 30 miles (48 km.) 

 which is the whole breadth occupied by the Quebec group 

 in this part, no rocks are exposed of a horizon lower than 

 a quartzite formation considered to underlie the Sillery." 

 By Logan, [4, p. 233] the Quebec group was tentatively 

 supposed to be of Lower Ordovician age. The quartzites 

 which were thought to underlie the Sillery are stated to 

 have, in other districts, conglomerates with pebbles of 

 limestone, associated with them. The Sillery was tenta- 

 tively assumed to form the upper member of the Quebec 

 group. 



In a succeeeding report [5, p. 4], Logan definitely divided 

 the Quebec group into three formations which, in ascending 

 order, were termed, Levis, Lauzon and Sillery. The Levis 

 formation was stated to be of about the horizon of the 

 upper part of the Calciferous (Beekmantown). 



In the years 1867 and 1868, James Richardson geologi- 

 cally mapped a large area on the south side of the St. 

 Lawrence, extending from above Levis northeastward to 

 beyond Riviere du Loup. In this general area, Richardson 

 concluded that besides formations belonging to the Quebec 

 group, there was also a development of measures uncom- 

 formably underlying the Quebec group and to these older 

 strata he applied the name Potsdam (Upper Cambrian). 

 [6, p. 120]. To the Potsdam were assigned the quartzites, 

 etc., which were described by Logan as occurring beneath 

 the Sillery in the Riviere du Loup district and elsewhere. 

 By Richardson the Potsdam was divided into three hor- 

 izons of which the upper was described as formed of light 

 coloured quartzite passing in places into grey, quartzose 

 sandstone, while in places black shales occur interstrat- 

 ified with the whole mass and at the base is a variable 

 thickness of conglomerate holding limestone pebbles. 

 This division of the Potsdam was stated [6, p. 128] to cross 

 Riviere du Loup in a narrow strip just below the High 

 Falls and to be succeeded down stream, by a lower division 

 of the so-called Potsdam. The escarpment which causes 

 the High Falls, was stated to be composed of Lauzon 

 (Quebec group) measures with probably a little of the 



