24 



undulating lowland. The central part of this dissected 

 lowland, like the coast in Cumberland and Colchester 

 counties in Nova Scotia, has been drowned by depression 

 beneath the sea, forming the Bras d'Or lakes. The 

 largest lake is separated from the ocean at its southern 

 end by a narrow strip of land only a mile wide. The long 

 arms of these lakes and of the peninsulas which separate 

 them are developed along the strike, respectively, of the 

 weaker Palaeozoic sedimentaries and the more resistant 

 granitic and metamorphic belts. Great Bras d'Or has a 

 depth of 350 feet (106 m.) ; Little Bras d'Or lake, 700 

 feet (215 m.). Not all this depth is necessarily due to 

 coastal subsidence since the late Tertiary dissection ; for the 

 island has been glaciated, and the amount of differential 

 erosion below sealevel may have been very considerable. 



ANNOTATED GUIDE. 



MONTREAL TO LEVIS. 



(G. A. Young.) 



Miles and 

 Kilometres. 



o. m. Montreal. Leaving Montreal, the Inter- 



o km. colonial railway (from Montreal to Ste. Rosalie, 



the Intercolonial runs over the Grand Trunk 

 railway) crosses the St. Lawrence river 

 and follows a general northeasterly course 

 through a district underlain by Palaeozoic 

 strata, mainly of Ordovician age. The district 

 traversed is a portion of the St. Lawrence low- 

 land or plain which extends far westward up 

 the valley of the St. Lawrence and the Great 

 Lakes. The northwestern portion of the plain 

 is underlain by an apparently conformable 

 succession of Ordovician strata dipping at very 

 low angles to the southeast. The oldest 

 measures are displayed along the borders of 

 the great Pre-Cambrian area to the northwest, 

 while the youngest beds outcrop towards the 

 centre of the plain. Though disconformities 

 presumably exist, the strata appear to afford 

 a complete section of the Ordovician system. 



