SECTION IV. 1882. f 39] 
IV.—Descriptive Note on a General Section from the Laurentian Axis to the Rocky 
Mountains north of the 49th Parallel. By Grorcr M. Dawson, D.Sc., F.G.S., &c. 
(Read May 26th, 1882.) 
The section in relation to which these notes are presented is a diagrammatic one, intend- 
ed rather to show the general arrangements of the rocks underlying the great plains, than 
the actual position of the beds on any definite line. The direction of the section is, however, 
almost exactly transverse to that of the main strike of the rocks, and that of the great 
interior continental valley which hes between the Laurentian Highlands on the east and 
the Rocky Mountains on the west. The section is about eight hundred miles in length. 
The profile represented by it is that of a line drawn from the middle of Lake Winnipeg 
west-south-westward, passing through the Touchwood and Poreupine Hills, and reaching 
the base of the Rocky Mountains, midway between the 49th and 50th parallels. The ver- 
tical scale and thickness of formations are necessarily very much exaggerated. 
Lake Winnipeg and the contiguous great lakes, with the low country about them, mark 
the outcrops of Silurian and Devonian rocks which lie at very low angles or are nearly 
horizontal. These rocks are, for the most part, magnesian limestones of pale buff colour, 
and resemble those representing these periods in the Mississippi Valley. They must have 
originally spread far up on the Laurentian plateau, and perliaps have inosculated with the 
similar rocks of the same age which border the basin of Hudson’s Bay. 
The great denudation which they have suffered, in times geologically very recent, is 
attested by the immense quantity of these peculiar rocks which, together with Laurentian 
and Huronian fragments, has been spread abroad over the surface of the great plains in the 
form of boulders and gravel. Rocks of Devonian age occupy the western portion of this 
region of the lakes, and Professor Hind has defined by observations in several localities a 
belt of them at least fifty miles in width. It is in connection with these rocks that the 
brine springs of the vicinity of Manitoba Lake occur. Salt has been manufactured from 
these for commercial purposes. 
North of the Winnipeg Lakes on the Arctic slope of the continent, the Devonian rocks 
appear to become more important in regard to the area they cover than the Silurian, and 
they are found to yield petroleum as well as salt. The description of the bitumen and 
mineral pitch of the Athabasca region, by Sir J. Richardson, would seem to indicate that a 
very important oil region there waits to be developed. 
The rocks consist of limestones and dark slates, and are referred by Meek—who has 
examined a considerable number of fossils from them—to the Hamilton and Genesee 
epochs. 
The “ black slate” of the Western and Southern States has been shewn to be the equi- 
valent there of the latter, and, according to Meek, “ holds exactly the same position with 
relation to the Hamilton beds as the Clearwater and Athabaska slates.” The resemblance 
of the rocks in these northern and southern localities, and the continued association of salt 
and petroleum with them to the south, renders it not improbable that, if reached by borings 
