38 



an expansion of the St. Lawrence river. Be- 

 tween Lachine and Ste. Anne de Bellevue, the 

 railway passes through a beautiful and highly 

 cultivated stretch of country, sloping gently to 

 Lake St. Louis. The great expanse of compara- 

 tively low flat land which borders the St. 

 Lawrence river from Montreal to Trenton is 

 underlain by the almost horizontal strata of 

 Upper Cambrian (Potsdam formation) and 

 Ordovician ages (Chazy, Calciferous, Black 

 River and Trenton formations) with the excep- 

 tion of the region between Brockville and King- 

 ston where this succession is interrupted by 

 granitoid gneisses and quartzites of Archean or 

 Pre-Cambrian age. Throughout the greater part 

 of this area, the underlying rock formations are 

 concealed by a heavy mantle of marine sands 

 and clays of Champlain age. This great 

 drift-covered Palaeozoic plain with its eminently 

 flat surface presents a strong contrast to the 

 uneven topography of the Archean rocky 

 plateau. The average elevation of this plain 

 in the vicinity of Montreal is about ioo feet 

 (30-5 m.), gradually rising westward until in 

 the vicinity of Central Ontario Junction, it is 

 almost 600 (183- m.) feet above the sea. 



232 -85m. Trenton. — (Grand Trunk Railway station). 



375-0 km. Alt. 280 ft. (85-3 m.) At Trenton the train is 

 switched from the Grand Trunk railway to the 

 Central Ontario railway, now being operated by 

 the Canadian Northern railway. 



Trenton. — (Central Ontario Railway station) 

 Alt. 258 ft. (78-6 m.). 



257 • 86 m. Canadian Pacific Railway Junction. — 



415-0 km. Alt. 598 ft. (182-3 m.) From the junction with 

 the Canadian Pacific railway, known also as 

 Central Ontario Junction.the railway runs north. 

 The main mass of Archean or Pre-Cambrian 

 rock is not reached until Bannockburn station 

 is approached. The transgression of the Pal- 

 aeozoic sea along this portion of the great 

 protaxis began early in Ordovician time. This 

 marine invasion was inaugurated by the shallow 

 water conditions resulting in the deposition of 



