Open Google Earth and type "Mont Saint Hilaire" into the search field...examine the three mountains near each other, especially Mont Yamaska...to me this would be the inverse of a crater chain, how they protrude out of the ground is just odd...there's nothing else like that around and the nearest mountain range is at least 70 - 75km away.
Mont Saint Bruno, which sits between Mont Royal and Mont Saint Hilaire, is clearly defined by an outer most circular scarring effect, but appears to have a lot more erosion than the other three, but the ring is quite visible.
The circular shape and topology is far too perfect for them to not have been part of some type of arc discharge, for at least one mountain (Yamaska), to be a function of standard geologic formation. Considering the electrical nature of volcanoes, not many people realize that Mont-Royal which sits right smack in the middle of Montreal is an extinct volcano...there has to be a connection.
These three mountains are very rich in minerals too according to Wikipedia...very rare minerals in some cases.
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 titanium-rich. Phlogopite is found as small metamorphic crystals in marble xenoliths within the syenite. Siderophyllite, a relatively rare mineral, occurs as large crystals in a metasomatised albite-rich albitite dike.
In addition to gabbro, the second intrusive suite included nepheline syenite, diorite and monzonite. The third intrusive occupies the eastern side and is mainly peralkaline nepheline syenites and porphyrites. The most mineralogically interesting are the associated agpaitic (alkali rich, low aluminium and silicon) pegmatites, the intrusive breccias, and the hornfels derived from the metasomatised sedimentary wall rocks. There have been over 366 distinct species of minerals collected at Mont Saint-Hilaire, 50 of which have this site as type locality.