[TYRRELL] PRESIDENTIAL ADDRESS 11 
Devonian 
In the vicinity of Nelson and Hayes rivers no evidence was 
observed of the presence of Devonian rocks, though away to the 
southeast, at the mouth of Albany river, Silurian limestones are 
conformably overlain by somewhat similar limestones of Devonian 
age, and it is not improbable that such rocks may have once existed 
on Nelson river and vicinity, but if so that they have since been 
eroded away. 
Carboniferous-Tertiary 
During this vast lapse of time, when the sediments which underlie 
the great plains of Saskatchewan- and Alberta, and which largely 
compose the Rocky Mountains, were being deposited in the sea, 
this country would appear to have been standing above sea level, 
for sedimentary rocks, which would undoubtedly have been deposited 
in the seas of those times where such seas existed, are entirely absent. 
It was, therefore, a land area and as such was subjected to processes 
of oxidation and erosion which softened and disintegrated the pre- 
viously formed rocks, and carried the disintegrated material down 
into the adjoining oceans. It was not only a land area, but it would 
appear to have been then as now very free from any violent orogenic 
or volcanic disturbances, for igneous rocks of Paleozoic or post- 
Paleozoic age are conspicuously absent. 
Just before the Pre-Cambrian rocks sank beneath the Ordovician 
sea, where Ordovician limestones were deposited on them, their 
surface had undoubtedly been reduced to a low-lying gently undulating 
peneplain. At the end of the Tertiary Period, after having been 
subjected to atmospheric and erosive influences since Devonian or 
Carboniferous times, the country had again been reduced to a gently 
undulating peneplain, the surface of which was undoubtedly weathered 
and softened to a considerable depth. 
Glacial 
While the surface of the land and the rocks underlying it were in 
the condition outlined above the Glacial Period began, and glaciers or 
ice-sheets accumulated on various points in Northern Canada and from 
these points spread out over the adjoining country. These ice-sheéts 
increased and decreased, appeared, disappeared, and reappeared in 
different localities as time rolled on. As they moved outwards from 
different centres over different parts of the country they scraped 
away from the surface all the decomposed and loose rock that had 
accumulated during preceding geological ages, and also removed a 
certain small quantity of the hard undecomposed underlying rock, 
