252 ROYAL SOCIETY OF CANADA 



Genekal Geology. 



Pleistocene. — A thick mantle of drift is everywhere present, this 

 consisting almost altogether of the debris transported and dropped by 

 the glaciers which once covered the district. The material is of a very 

 diversified character, ranging in composition from the old Lanrentian 

 sediments and intnisives, down to the breccia, one of the youngest rocks 

 known to be present in the district ; the variation in size is also extreme, 

 from boulders of a ton in weight down to fine clays. The district having 

 undergone a period of submersion since the retreat of the glaciers, the 

 glacial materials have to a certain extent been rearranged as beach de- 

 posits in lines representing former water levels. These beaches are well 

 marked on the various mountains and are found at a considerable eleva- 

 tion above sea level, a well known example being that found in the Cote 

 des Neiges Cemetery at Montreal. 



Paleozoic Sediments. 



riie Devonian and Silurian are represented solely by inclusions in 

 the breccia of Ste. Helen's Island, and will be more fully discussed later 

 when treating of the age of the breccia. The Ordovician is represented 

 by the Utica, Trenton, Chazy and Calciferous formations. 



Utica. — The Utica is found chiefly on the south side of the 

 St. Lawrence, but forms a narrow belt on the island of Montreal at 

 Verdun and Point St. Charles. It is present on Ste. Helen's Island, and 

 is dredged up from the bottom of the harbour. A remnant is found 

 adhering to the east side of Mount Eoyal above the High Level Eeservoir. 

 The rock is composed of a rather soft, friable, dark coloured bituminous 

 shale, which weathers rapidly to very small angular fragments. 



Trenton. — The Trenton group is by far the most important series 

 on the island of Montreal, since it occupies three-fourths of the whole 

 area. It consists of dark coloured, compact, somewhat bituminous lime- 

 stone, in beds commonly one foot thick and occasionally as much as three. 

 A flat anticlinal arch striking west-northwest from Mount Eoyal has been 

 eroded, exposing the underlying Chazy. Other subordinate anticlinals 

 form the backbone of He Jesus and of the west end of the Island of 

 Montreal. These features account for the extremely irregular boundaries 

 shown by the lower contact of this series. 



Chazy. — This formation is made up of beds of massive limestone, 

 sometimes magnesian and generally of a gray colour. The rock is com- 

 monly of a granular or crystalline character owing to the crystallisation 

 of the very abundant enclosed fossil remains. This formation, crossing 

 the Island of Montreal and He Bizard in a narrow belt, underlies the 



