Monteregian Hills


The Monteregian Hills is a linear chain of isolated hills in Montreal and Montérégie, between the Laurentians and the Appalachians.

Etymology

The first definition of the Monteregian Hills came about in 1903 when Montreal geologist Frank Dawson Adams began referring to Mount Royal and hills of similar geology in the Saint Lawrence Lowlands as the "Royal Mountains". Other hills in the chain included Mont Saint-Bruno, Mont Saint-Hilaire, Mont Saint-Grégoire, Mont Rougemont, Mont Yamaska, Mont Shefford, and Mont Brome.
It was only later that Mont Mégantic, the Oka Hills, as well as the Saint-André and d'Iberville formations, were added to the list.

Geology

Each hill in the chain consists of an erosional remnant of Cretaceous intrusive igneous rock and associated hornfels, which are more resistant to weathering than the surrounding sedimentary rock. All of the hills have dark-coloured mafic rock such as gabbro and essexite; some also have large areas of pulaskite, syenite, and other light-coloured rock.
The Monteregian Hills are part of the Great Meteor hotspot track, formed as a result of the North American Plate sliding westward over the long-lived New England hotspot, and are the eroded remnants of intrusive stocks. These intrusive stocks have been variously interpreted as the feeder intrusions of long extinct volcanoes, which would have been active about 125 million years ago, or as intrusives that never breached the surface in volcanic activity. The lack of an obvious track west of the Monteregian Hills may be due either to failure of the plume to penetrate the Canadian Shield, to the lack of recognizable intrusions, or to strengthening of the plume when it approached the Monteregian Hills region. However, there is evidence the hotspot track extends northwestwards, including epeirogenic uplift, mantle velocity anomalies and kimberlitic volcanic features that become older away from the Monteregian Hills.
The shallow, rocky sandy loam soils of the summits are mostly covered in forest. Where the underlying rock is rich in olivine, as over large areas of Mont Saint-Bruno and Mont Rougemont, these soils are classed as dystric brunisol. Podzol tends to develop over rock which lacks olivine, although many of these podzols lack an eluvial horizon. Lower slopes are covered with aprons of gravel or sand. The sandy soils are usually podzols with classic Ae development; they often have subsoil hardpan and are undesirable for agriculture. The free-draining gravels are preferred for apple orchards, which grow in thermal belts where cold air can drain to the valley floor.
NameHeightAgeCoordinatesLocation
St. Andrews formationn/a45°55"N, 74°31'WSaint-André-d'Argenteuil
Oka Hillsn/a45°28'N, 74°5'WOka
Mount Royal118-138 myr45°30'23"N, 73°35'20"WMontreal
Mont Saint-Bruno118-136 myr45°33'1"N, 73°19'09"WSaint-Bruno-de-Montarville
Mont Saint-Hilaire135 myr45°33'8"N, 73°9'3"WMont-Saint-Hilaire
Mont Saint-Grégoire119 myr45°21'29"N, 73°09'08"WMont-Saint-Grégoire
Mont Rougemont137 myr45°28'36"N, 73°03'17"WRougemont
Mont Yamaska120-140 myr45°27'25"N, 72°52'19"WSaint-Paul-d'Abbotsford
Mont Shefford120-130 myr45°21'49"N, 72°37'33"WShefford
Mont Brome118-138 myr45°16'59"N, 72°37'59"WBromont
Mont Mégantic128-133 myr45°27'20.5"N, 71°9'7.6"WNotre-Dame-des-Bois

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