AbstractsEarth & Environmental Science

The detailed geology of an area south of Cote des Neiges road in Westmount, P. Q. was mapped and correlated with that of two adjoining areas, which had been already studied. The major plutonic rock is essexite, which represents the south-west extention of the main Mount Royal intrusive. On the western contact, between the essexite and the Trenton limestone, an intrusion of syenite outcrops, which is cut by younger syenite dikes. The Trenton limestone, essexite, and older syenite are cut by numerous lamprophyre dikes such as camptonite, monchiquite, fourchite, and leuco-lamprophyres. Aplite dikelets and dikes of a composition similar to essexite were found intruding the essexite rock. A short description of the St. Lawrence Lowlands Province and the Monteregian Petrographic Province is given in the first part of tile thesis, as both are represented in the area. This is followed by a discussion of the process of intrusion and the origin of the Mount Royal plutonics. Samples were taken of all rock types and studied in thin section. The megascopic end microscopic description of the rocks as well as their field relations is given in the second part on petrography.