10 
MUSEUM BULLETIN NO. 11. 
Soil Covering. 
The soil covering upon the upland does not as a rule grade 
into weathered rock below, but seems to have been transported 
there from its original source. That it is transported material 
is confirmed by the foreign boulders scattered through it. This 
covering, which consists of sand, clay, and boulders only rarely 
stratified, is irregular in thickness but is in general thin. It has 
been ascribed to deposition from a continental ice sheet which 
at one time covered the country and which scoured soil and rocks 
off one part of the plateaus and deposited them on another. 
Large terraces found to elevations of over 5,000 feet above sea- 
level are supposed to be sediments laid down in lakes formed 
during the retreat of the ice sheet. 1 
Drainage upon the Upland . 
The drainage upon the upland is by means of wide shallow 
valleys which show a certain amount of rectilinearity in plan, 
and parallelism between adjacent valley stretches. In this 
respect they resemble the deep valleys which lie below them, and 
we shall discuss their relations more fully under the heading of 
“Valleys”, p. 13. Many small lakes and swamps are found 
within these shallow troughs. Some of them are rock basins 
and others seem to be partly held up by dams of glacial debris 
at their lower ends. 
Relations between Topography and Structure. 
The relations of topography to structure are of particular 
interest from a theoretical standpoint since they form one of the 
more delicate criteria by which one may judge to what stage a 
landform has progressed in its gradual evolution through the geo- 
graphic cycle. We found a partial accordance of the upland 
14 ‘On the later physiographicat geology of the Rocky Mountain region 
in Canada, with special reference to changes in elevation and to the history 
of the Glacial Period,” by G. M. Dawson. Trans. Roy. Soc. Canada, vol. 8, 
No. 4, 1890, pp. 3-74, 
