386 DR. J. W. DAWSON ON THE GEOLOGY OF THE 
this way, but must mark the margin of an ancient glacial sea, Or 
at least of that deeper portion of such sea in which heavy ice could 
float, while in its upper portion it shows evidence of having been, 
in the later periods of its formation, an actual water-margin. 
The railway, taking advantage of the oblique valley of Thunder 
Creek, crosses the coteau at one of its least-marked portions, but 
where it still presents very definite and striking characters. On 
entering it, the railway passes for nearly 30 miles through a roll- 
ing or broken country, consisting of successive ridges and mounds 
interspersed with swales and alkaline ponds without outlet. To this 
class belongs a somewhat extensive series of lakes known as 
the ‘‘ Old Wives’ Lakes.” The highest point of the coteau on this 
section appears to be near Secretan Station. 
As seen in the road-cuttings, the basis of the ridges appears to 
consist of thick beds of imperfectly stratified clay, derived from the 
disintegration of the local Cretaceous beds, but with many Lauren- 
tian boulders. In one place the clay was observed to be crumpled 
as if by lateral pressure. Above the clay are stratified gravels, 
also with large boulders, most abundant at top. The ridges are 
highest and most distinct at the eastern or lower side, and gradually 
diminish towards the upper or western margin, where they termi- 
nate on the broadly rolling surface of the upper prairie. 
The history of the coteau would seem to have been as follows :— 
1. The excavation in pre-glacial times of an edge or escarp- 
ment in the gently sloping surface of the Cretaceous and Laramie 
beds, and the cutting by subaerial causes of coulées and valleys 
of streams in this escarpment. 
2. Submergence in the glacial period, in such a manner as to 
permit heavy ice loaded with Laurentian débris to ground on the 
edge of the escarpment and deposit its burden there, while at the 
period of greatest submergence deep water must have extended 
much further westward. These conditions must have continued for 
a long time and with somewhat variable depth of water. 
3. Re-elevation, during which gravel ridges were formed, until at 
length the coteau became the coast-line of a shallow sea, which 
lingered at a later date along the line already referred to in advance 
of the coteau. , 
4. On the re-elevation of the country, the transverse ravines and 
_ valleys were so effectually dammed up by the glacial ridge, that the 
surface waters of the region, now comparatively arid, have to remain 
as alkaline lakes and ponds behind the coteau. 
The upper prairie plateau, extending from the coteau to the 
Rocky Mountains, has, on its general surface, comparatively few 
boulders ; yet these are locally numerous, especially on the eastern 
and northern sides of some gentle elevations of the prairie. They 
consist, as before, of Laurentian gneiss, Huronian schists, and yellow 
Silurian limestone, all derived from the eastern side of the plains, 
some of the boulders of Laurentian gneiss being of great dimen- 
sions. Some of these have been used in modern times by the 
