
GLACIAL PHENOMENA AND SUPERFICIAL DEPOSITS. 249 
lower layers of the deposit, are as a rule the finest and most uniformly 
stratified. Those near the surface, though rarely showing any material so 
coarse as to be called sand, sometimes take the form of moderately coarse 
arenaceous clay. A portion of these upper layers may have been formed 
by the overflow of the river itself, after the recession of the lake. Pebbles 
or boulders of any kind are exceedingly rare, and where seen were pro- 
jecting above the surface of the soil. The total number observed in all 
my excursions in this valley, might almost be counted on the hand. 
They are usually of Laurentian origin, though one or two of limestone 
were met with. 
575. The depth of the alluvial deposit near the forty-ninth parallel, 
has not been ascertained, it is, however, certainly greater than the depth 
of the immediate valley of the river, where asection of from thirty-five 
to forty feet is exposed. Some of the lower and finer beds are often, 
twisted and bent, though not showing any evidence of false bedding. 
This I can only attribute to the action of floating ice-cakes in the 
former lake. Small flattened nodules are occasionally found forming 
horizontal lines in the deposit. Though deep and very uniform in the 
centre of the valley, the alluvium does not maintain the same homo- 
geniety on approaching the sides, and these appear to have been occupied 
by banks and shoals of rather coarser materials. Several miles before 
reaching the base of Pembina Mountain, on the West, the subsoil is found 
to contain small rolled pebbles, of which the greater part are derived 
from the clay-shales of the Pembina Mountain group. Nine miles from 
the base of the mountain, a well, dug eight feet deep, passed for that 
depth through very fine, clean, silicious sand. Occasional thin layers 
holding coarser particles occur even in the centre of the valley. One 
which was called a “sand,” when the argillaceous matter was washed 
away, was found to consist of very minute rounded fragments of the 
Cretaceous clay-shales above mentioned. 
576. The typical deposit, however, where I have examined it, in the 
vicinity of Red River, is a fine yellowish marly and arenaceous clay, holding a 
good deal of calcareous matter, and effervescing freely with an acid. Under 
the microscope the coarser siliceous particles, in their average size, vary 
from 0-002 to 0:001 of an inch in diameter, and there is much formless 
argillaceous matter. 
From the occurrence of recognisable fragments of Cretaceous No. 4 
in many places, it is probable that rocks of the Cretaceous series may 
have contributed largely to the formation of the alluvium, as indeed 
