769 
of about sixty feet, and their surface was slightly raised, but the 
front of each terminated ina blunt point which projected in the 
middle and in the lower part. As these great double-acting plough- 
shares advanced, they turned up, Mr. Logan says, the soft mud from 
the bed of the river, casting it on the banks, and producing so into- 
lerable a stench that no one could approach within 100. yards. This 
odour, he conceives, arose from the sulphuretted hydrogen produced 
by the decay of vegetable matter. 
No sooner was this dam formed than the waters of the Maskinongé 
began to rise, and the houses, with every other thing composed of 
wood throughout the whole of the nine miles to the granitic hills, were 
set afloat. It was two days, however, before the lake thus formed 
overtopped the barrier; but by October it had transported into Lake 
St. Peter so great a portion of the débdcle that the river was not 
more than ten feet above its ordinary level. 
When Mr. Logan examined, in the subsequent autumn, the spot 
where the slip took place, the bottom of the widest part of the chasm 
was thirty feet below the level of the surrounding country ; and about 
400 yards from the river, where the disturbed district narrowed, there 
was a sudden additional descent of fifteen feet. From this point the 
ground sloped gently to the water’s edge. The only vestiges of the 
original surface then visible, were a few patches of grass, and occa- 
sionally twenty or thirty yards of wooden fence, the superficies being 
composed of parallel mounds three or four feet high, and which over 
the central portion of the area ranged at right angles to the axis of 
the slip, but along the sides conformably with the bounding outline. 
A circumstance connected with the form of the disturbed district 
Mr. Logan considers worthy of attention. Around the whole of the 
area, except the most northern extremity, there was, previous to the 
slip, a depression of the surface, due on the eastern side to the slope 
of the right bank of the river, and a tract of low land; and on the 
western side to a dingle traversed by a brook. After the slip, a ridge, 
not many feet wide, remained between these lower surfaces and the 
chasm, forming a marginal rim which was broken through at only 
one point, where it was intersected bya dingle which united with the 
one on the western side. 
The cause of the slip, Mr. Logan is of opinion, was pressure on an 
inclined plain, assisted by water ; and though he was not able to de- 
termine the nature of the subsoil, he is of opinion, from a survey of 
the surrounding country, that it consists of the Silurian limestone, 
the dip of which, where visible, is in the direction of the slip. 
If boulders were at the bottom of a mass moved in the manner of 
the Maskinongé slip, it is easy to see, Mr. Logan observes, that 
parallel grooves and a polish on the surface of rocks may not, in all 
cases, be due to the agency of ice. 
3. Marine Shells on Montreal Mountain.—After alluding to Mr. 
Lyell’s account of the fossil shells collected by Capt. Bayfield * in the 
* Ante, p.119 (April 24, 1839), and Geol. Trans., 2nd Series, vol vi. 
p. 135. 
