768 
quartzose conglomerate, which crops out from beneath the limestone, 
and is succeeded by pyritiferous clay-slate. The cleavage of this 
formation is stated to be from N.E. toS.W., or parallel to the general 
strike of the beds. 
Between Montreal and Lake St. Peter, the banks of the St. Law- 
rence have generally a height of twenty or thirty feet above the level 
of the water, but the plains near the margin of the river are occa- 
sionally so low as to permit the formation of marshes, and on the 
southern side the general surface does not apparently attain the same 
altitude as on the north-western. On this side, at a distance varying 
from one to six miles from the St. Lawrence, there is a sudden rise 
of 100 feet, forming the boundary of a terrace which extends to the 
granitic hills, where a second rise takes place of 200 or 300 feet. 
The terrace, composed of soft materials, has avery even surface over 
a great area, being only modified by the protrusion, at a few places, 
of the Silurian limestone. It is however intersected by the rivers 
which flow from the granitic range, and which, dashing down from the 
hills, cut at once into the terrace, nearly to the level of the St. Law- 
rence. The banks of these tributaries are liable to landslips, and an 
extensive one which occurred on the Maskinongé in 1840 is described 
in this part of Mr. Logan’s paper. 
The waters of that river, after passing through a series of lakes, are 
precipitated from the granitic region in a beautiful cascade, and then 
flow along a deep valley in the terrace, the only interruption to their 
course being a collection of boulders Eombmned with a mill-dam, pro- 
ducing a fall of about fifteen feet. The valley has a uniform breadth, 
the distance between the summit of the banks being about 200 yards, 
and the height of the banks is 120 feet. 
The point at which the landslip occurred is nine miles from the 
granitic hills, and where the river, ten to twenty yards wide, changes 
its direction from south to west, for 700 yards. The movement com- 
menced about eight o’clock on the morning of the 4th of April 1840, 
and when the winter snow was still on the ground. ‘The mass of 
marly clay, first detached, was about 200 yards in breadth‘and 700 in 
length; and it was followed, at intervals of a few minutes, by four 
others. The whole of the area thus affected amounted to about 
eighty-four acres,and the total length was 1300 yards; but the breadth 
varied, the narrowest part being nearest to the river, and the widest, 
equalling 600 yards, a considerable way from it. The moving mass 
first crossed the stream, and then splitting against the opposite 
bank, where it averaged a thickness of seventy-five feet, one-half 
turned up the valley for about three-quarters of a mile, and the other 
half down it for an equal distance, forming a dam half a league in 
extent. The whole operation was completed in about three hours. 
For some time after the movement began the surface of the great 
masses remained unbroken, and the sugar maple-trees, with which 
they were covered, preserved, for the greater part, an erect position. 
Two farm-steads were also carried away, and though the people 
escaped, tne cattle, and other live stock perished with the falling 
buildings. The masses which moved along the valley had a height 
