[HOWARD] SOME OUTLIERS OF THE MONTEREGIAN HILLS 



51 



Quaternary 

 Palaeozoic 



(Champlain sands and clay 



Boulder clay 



Monteregian Intrusives 



Silurian and Devonian (present as fragments in 

 breccias) 



Ordoviciaji 



Utica shale 



Trenton limestone 



Black River formation 



Chazy limestone 

 ^Beekmantown or Calciferous dolomitic limestone 



Cambrian 



Potsdam sandstone 



I Anorthosite 

 Pre-Cambrian \ Laurentian granites and gneisses 



Grenville Series, limestones and quartzites 



Pre-Camhrian 



[( 



Anorthosite. — Near Cartierville on the Island of Montreal is a 

 small area underlain by anorthosite, identical with the Morin anor- 

 thosite. 



Laurentian and Grenville Series. — The area to the north of the 

 St. Lawrence lowlands is underlain by a complex series of Pre-Cam- 

 brian rocks including the Grenville Series of quartzites and crystalline 

 limestones together with highly metamorphosed sediments in the 

 form of schists and gneisses. The whole area was intruded by Lau- 

 rentian granites and gneisses. In the Oka Mountains there is an 

 outlier of Grenville limestones and quartzites intruded by Laurentian 

 granites and gneisses. 



Palœozoic 



Cambrian. Potsdam Sandstone. — This formation which consists 

 of a fine-grained, light-coloured, highly siliceous sandstone is found 

 on the islands and west shore of Lake St. Louis, on the south-west 

 shore of the Lake of Two Mountains as far as Rigaud, and also on 

 the north shore of this lake flanking the Pre-Cambrian outlier of the 

 Oka Mountains. 



Ordovician. Beekmantown or Calciferous Formation. — This re- 

 presents a transition stage between the Potsdam and the Chazy 

 limestones, and is a granular magnesian limestone or dolomite. 



