GEOLOGICAL AUEAS OP CA>rADA, 95 



mountains, wliich rise abruptly from the generally level surface of 

 the district in the more southern and western portions of its area ; 

 and in addition to these Silurian and eruptive rocks, Glacial and 

 Post-Glacial accumulations, with deposits of comparatively modern 

 origin, occur throughout the district generally. 



The Potsdam beds consist of coarse conglomerates and fine-grained 

 siliceous sandstones — the latter in many localities sufficiently pure 

 for glass-manufacture and for the hearths of furnaces. The formation 

 is largely displayed in Hemmingford Mountain, and over large portions 

 of Huntingdon, Chateaugay, and Beauharnois, from whence it crosses 

 the St. Lawrence, and spreads over a large part of Soulanges and 

 Vandreuil ; and from thence, passing across the western end of the 

 Island of Montreal and Isle Bizard, it wraps around a large outlying 

 mass of Laurentian gneiss (forming Mount Calvaire on the north 

 shore), and continues uninterruptedly along the edge of the Laurentide 

 district as far east as the River Chicot, where the continuity of the 

 strata is broken by a fault, and limestones of the Trenton formation 

 are let down against the Potsdam beds. East of this point, the 

 formation only appears at one or two places — notably on the St. 

 Maurice, where it exhibits a slight thickness of nearly horizontal 

 beds of conglomerate and sandstone, resting upon gneiss. Throughout 

 its range, as far east as the Chicot, it is accompanied by sandy and 

 dolomitic limestones of the Caleiferous formation, and these cover 

 large areas south of the St. Lawrence, and in the country around the 

 junction of the St. Lawrence and Ottawa. East of this formation, on 

 the south side of the St. Lawrence, limestones of the Chazy and 

 Trenton series, and dark bituminous shales of the Utica formation, 

 with succeeding sandstones and arenaceous shales of the Hudson 

 River formation largely prevail — the latter, especially, east of Richelieu 

 River. These formations cross the St. Lawrence, and range in regular 

 sequence along the north shore between the Caleiferous outcrop and 

 the river bank. The intervening Island of Montreal, Isle Jesus, Isle 

 Bizard, &c., consist essentially of Chazy, Trenton, and Utica strata — 

 the Hudson River beds coming up farther east. The Chazy limestones 

 of Caughnawaga and St. Dominique on the south shore, those of Ste. 

 Genevieve on the Island of Montreal, of Isle Bizard, and of St. Lin 

 on the north shore, yield marbles (red-spotted or uniformly red) of 

 good quality. East of the River Chicot, which enters the St. 

 Lawrence on the north shore, near the upper or western extremity of 



