| "Mount Royal | 769.6 feet. | |
| Montarville or St. Bruno | 715 " | (O'Neil) |
| Belœil | 1,437 " | (Leroy) |
| Rougemont | 1,250 " | |
| Yamaska | 1,470 " | (Young) |
| Shefford | 1,725 " | |
| Brome | 1,755 " | |
| Mount Johnson or Monnoir | 875 " |
"They have been called the Monteregian Hills from Mount Royal ('Mons Regius'), which is the best known member of the group and may be taken as their type.
"Brome Mountain is by far the largest member of the group, having an area of 30 square miles. Shefford comes next in size, having an area of rather less than nine square miles; while Mount Johnson, which is very much smaller than any of the others, has an area of only .422 of one square mile.
"Of these eight, the first six, as Logan notes, 'stand pretty nearly in a straight line,' running approximately east and west, Mount Royal being the most westerly, and the others following in the order in which they are enumerated above, until Shefford Mountain, the most easterly member of the series, is reached. Mount Johnson and Brome Mountain lie on a line parallel to them, a short distance to the south, Rougemont being the nearest neighbour to Mount Johnson and Brome Mountain immediately south of Shefford. It is highly probable, in view of this distribution, that these ancient volcanic mountains are, as is usual in such occurrences, arranged along some line or lines of weakness or deep-seated fracture. The 'pretty nearly straight line' referred to by Logan, on which the first six mountains of the group are situated, must be considered either as a single line with a rather sharp curve in the middle or as made up of two shorter straight lines, each with three mountains, diverging from one another at an angle of about thirty degrees, with Montarville at the point of intersection. Mount Johnson and Brome Mountain might then be considered as situated on short subsidiary fractures.
"The distance from Brome Mountain, the most easterly member of the Monteregian Hills, to Mount Royal the most westerly, is 50 miles (80 km.). For a few miles to the east and west of these mountains respectively, however, evidences of the igneous activity of the system are manifested in the occurrence of occasional dykes or small stocks of the consanguineous rocks of the series, the extreme easterly representative of these being a little stock exposed about a mile and a half east of Eastman, on the line of the Canadian Pacific Railway, and the most westerly being a series of dykes and a small stock at La Trappe, on the Lake of Two Mountains. Similarly, the most northerly extension is represented by a sheet intercalated between strata of the Chazy limestone in the bed of the Little River, near St. Lin, 15 miles (24 km.) north of St. Lin Junction. It is difficult to say just how far to the south the last evidences of the Monteregian activity are found, but scattered dykes of bostonite, camptonite and monchiquite have been described by Kemp and Marsters from the shores of Lake Champlain (out of which flows the River Richelieu), to a distance of 90 miles (145 km.) or more south of Mount Johnson.
"The Monteregian Hills are a series of ancient plutonic intrusions. Some of them (e. g. Brome Mountain) are apparently denuded laccoliths, one of them (Mount Johnson) is a typical neck or pipe, and it is probable that some, if not all, of them, represent the substructures of volcanoes which at one time were in active eruption in this region.
"It is impossible to determine accurately the date of these intrusions. In the case of Mount Royal, however, inclusions of Lower Devonian limestone are found in the intruded rock, so that the intrusions forming the mountain are later than Lower Devonian time.
"Since Dresser by another line of evidence, has shown that the intrusion of Mount Shefford probably took place before late Carboniferous time, the Monteregian intrusions probably date back to the late Devonian or early Carboniferous period.
"It must be noted that while six of these mountains rise from the horizontal strata of the plain, the two most easterly members of the group, namely Shefford and Brome, while still to the west of the axis of that range, lie well within the folded belt of the Appalachians, although, owing to the extensive denudation from which the region has suffered, this folding has had but little influence on the local topography. About La Trappe, at the extreme westerly extension of the Monteregian area, the dykes of the series cut rocks of Laurentian age, which here form an outlier of the great Laurentian protaxis on the north.