Geological Society of London. 37 
2. “On'the Superficial Geology of the Central Plateau of North- 
western Canada.” By J. B. Tyrrell, Hsq., B.A., F.G.S., Field 
Geologist of the Geological and Natural History Survey of Canada. 
The Drift-covered prairie extends from the west side of the Lake 
of the Woods to the region at the foot of the Rocky Mountains, 
rising from a height of 800 feet on the east to 4500 feet on the west, 
the gentle slope being broken by two sharp inclines known as the 
Pembina Escarpment and the Missouri Coteau, giving rise to the 
First, Second, and Third Prairie Steppes. 
The author described the older rocks of this region, referring 
especially to his subdivision of the Laramie Formation into an 
Edmonton Series of Cretaceous age, and a Pascapoo Series forming 
_ the base of the Eocene, and then discussed the Superficial Deposits 
in the following order :-— 
1. Preglacial gravels occurring along the foot of the Rocky 
Mountains, composed of waterworn quartzite pebbles, similar to 
those now forming and, like them, produced by streams flowing from 
the mountains. 
2. Boulder-clay or Till, having an average thickness of 50-100 
feet, and filling up pre-existing inequalities. The clay is essentially 
derived from the material of the underlying rocks. The smoothed 
and striated boulders of the western region are largely quartzites 
derived from the Rocky Mountains; these gradually disappear 
towards the east, and are replaced by gneisses and other rocks 
transported from the east and north-west. Towards the north-west 
several driftless hills over 4000: feet high appear to have stood as 
islands above the sheet of ice. Some of the surface erratics of 
gneissose rock have doubtless been derived from the Till, whilst 
others are connected with moraine deposits, and others, again, appear 
to have been dropped from bergs floating in seas along the ice-front. 
The Till is sometimes divisible into a lower massive and upper 
rather stratified deposit, separated occasionally by 
3. Interglacial Deposits of stratified material, with seams of im- 
pure lignite, and shells of Pisidium, Limnea, Planorbis, etc. 
4. Moraines, which are intimately associated with the Boulder-clay, 
and represent terminal moraines of ancient glaciers which originated 
upon or crossed the Archean belt. One of these is the well-known 
Missouri Coteau. 
After pointing out the derivation of quartzite pebbles in the drifts 
of the eastern region from Miocene conglomerates, and not directly 
from the Rocky Mountains, the author described 
5. The Kames or Asars generally occurring at the bottoms of wide 
valleys, and which resemble in structure those of Scandinavia. 
6. Stratified Deposits and Beach-ridges which have been formed 
at the bottoms and along the margins of freshwater-lakes lying 
along the foot of the ice-sheet. The principal of these occupied the 
valley of the Red River, and has been called Lake Agassiz ; it had a 
length of 600 miles and a width of 170 miles. The author described 
in detail the gravel terraces formed around this lake, and showed 
that a slow elevation had taken place towards the north and east 
