range from in elevation. Cliffs The best-known feature of the mountain is the cliffs. Collectively known as the falaise dieppe, or falaise de Dieppe (Dieppe cliffs) the cliffs are part of the Dieppe summit, and nearly high. Some of the best known features of the cliffs include the 60-metre high Tour rouge (Red tower), as well as two slabs, the Dalle noire (Black slab) and Dalle Verte (Green slab), which rise at a 75-degree angle. The cliff's unique ecosystem hosts lichens, as well as cedar trees, some of which may be as much as five hundred years old. It also hosts the mountain's population of peregrine falcons. However, the action of rock climbers has proven destructive to the ecosystem, in addition to being dangerous to the climbers themselves. A white cross on the cliff commemorates the death of a boy scout in 1941. Lac Hertel At the centre of the mountain is Lac Hertel, a lake in a glacially-formed depression in the middle of the various summits. It covers an area of , and has a maximum depth of . It is fed by three permanent streams; a fourth flows from the lake toward the Richelieu River. The lake serves as a secondary reservoir of drinking water to the region, and, as such, swimming, fishing and boating are forbidden. The central position of the lake on the mountain has led to claims that Mont Saint-Hilaire is a volcanic caldera. However, the lake is actually the result of glacial erosion, and in no way an ancient volcanic crater. Geology Mont Saint-Hilaire is one of the Monteregian Hills, a group of erosional remnants of intrusive mountains spread across southern Quebec. It is composed of three distinct plutonic intrusions that formed during the Cretaceous Period between 133 and 120 million years ago. Like the other Monteregian Hills, Mont Saint-Hilaire forms part of the Great Meteor hotspot track, which was created when the North American Plate slid over the New England hotspot. During this time, melting occurred, creating subsurface magma intrusions. Erosion of the surrounding softer sedimentary rocks revealed the more resistant rocks of Mont Saint-Hilaire. Mineral wealth Mont Saint-Hilaire is a famous mineral locality because of its great number of rare and exotic mineral species. Annite (iron rich biotite) from Mont Saint-Hilaire is among the most iron-rich found in nature. In the gabbro, biotite is less iron-rich, has lower manganese content, but is