Geology of Montreal, Province of Quebec, Canada

Abstract

Situated on an island at the confluence of the St. Lawrence and Ottawa rivers in the Province of Quebec, Montreal has been a gateway to western exploration and commercial development ever since its discovery in 1535 and its founding as Ville-Marie in 1642. Nowadays, it is still a major Canadian transportation centre. The area lies within the St. Lawrence Lowlands, between the Precambrian Shield to the northwest and the Appalachians to the east, and is underlain by slightly deformed and faulted sandstone, carbonate rocks and shales of Cambro-Ordovician age. Mount Royal, the large hill from which the city takes its name, is one of a series of Mesozoic plutons that intruded the sedimentary rocks. Surficial deposits are of Wisconsin age or younger, and include tills, interstadial silts and sands, marine clay, marine and estuarine beach materials and recent peat deposits. There are no significant geological constraints to development in the area. Overburden materials present designers with a range of foundation conditions in terms of bearing capacity, settlement and the control of excavation stability but most major constructions are founded on rock. Investigation and design techniques combine the latest in both European and American practice but remain conventional. Environmental concerns related to the geology proper are not very significant. The seismicity of the area is relatively high. Montreal is near the centre of a broad zone, classified as No. 2 on the 0 (most stable) to 3 Canadian system, that covers most of southern Quebec. The bedrock formations have historically furnished the city with a cheap and abundant source of building materials and the presence of rock close to surface has led to the extensive use of rock tunnels for water supply, trunk sewers and for the “Metro” subway and stations into Montreal9s “under-ground city” that provides a haven in winter for downtown workers and shoppers. Montreal hosts a large and active geotechnical community, becoming increasingly more involved in all local development projects. The paper is presented in SI units, now used exclusively in Canada.