32 
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 mani- 
fested 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 accompanying map embraces the entire region 
affected by the intrusions of the Monteregian Hills, so far 
as its eastern and western extension is concerned: while 
beyond the limits of the map, to the north and south, the 
occurence of scattered dykes occur as has been noted, which, 
from their petrographical character are believed to be re- 
lated to these intrusions. 
The Monteregian Hills are a series of ancient plutonic 
intrusions. Some of them (e.g. Brome mountain) are ap- 
parently 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 moun- 
tain 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 intru- 
sions probably date back to the late Devonian or early 
Carboniferous period. 
