14 
also the basin of the Peace below the site of Vermilion, and the lower 
Athabaska flood-plain. The entire basins of Athabaska and Claire lakes 
were submerged, and the eastern shore was the margin of the Laurentian 
highland. The flat-lying country of the Salt Plains southwest of Fort 
Smith probably originated as the bottom of this lake. 
As the general water level lowered to form the 800-foot lake, a part of 
it seems to have been maintained in the present Moose Lake basin, at the 
foot of Caribou mountains, by the damming of Jackfish and Little Buffalo 
rivers. The morainic system above described served to pond the Little 
Buffalo, and morainic ridges of uncertain origin, across the Jackfish, held 
back the waters of the latter stream. The drainage of the basin has gone 
on until very recent times and se.ems to be still in progress (13, 56). Its rate 
has been determined by the rate at which the streams have been able to cut 
through the barriers. 
The 700-foot level is practically that of Athabaska lake. The basins of 
Athabaska and Great Slave lakes were then separated, the former having 
a northern arm extending down Slave river about half-way to Smith 
rapids, and the latter having a great southern arm occupying the site of 
the lower Slave and Little Buffalo river flood-plains. In subsequent post- 
Glacial time the extensions of the two lakes have been silted full to form 
wide flood-plains in which the streams take sluggish, meandering courses. 
The manner in which these plains were formed has been well summarized 
by E. M. Kindle of the Geological Survey, Canada (33). Mr. Kindle 
notes particularly the immense amount of drift timber and silt brought 
down by Athabaska and Peace rivers, with the localization of the deposits 
of this material in the western end of lake Athabaska and on the south 
shore of Great Slave lake. A more detailed description of the lowlands 
will be found with the discussion of their vegetation. 
Although no precise lines can be drajvm, the distribution of the clayey 
and sandy soils on the Alberta plateau seems to be correlated with the 
main morainic systems. In the retreat of the ice eastward from Caribou 
mountains, moraines were left on the slopes of the mountains and in the hill 
country described between the Ninishith and Moosehorn Slough districts. 
Outwash from the latter front would tend to deposit its finer materials 
farther to the westward than the coarser ones. The clayey deposits at 
the base of the mountains may have originated in this way. To the east- 
ward they disappear in the sand and gravel country south of Moose Lake 
basin. Similar soils found from the Pine Lake-Lane Lake district to Flat- 
grass lake may have had a similar origin in some lake stage that existed 
immediately after the retreat of the ice eastward from the moraines that 
lie just west of them. 
CLIMATE 
Insufficient data are available for the interpretation, except in a general 
way, of climatic factors in their relation to the vegetation. For many years 
records of precipitation and temperature have been kept at various settle- 
ments, but as there are very few evaporation or frost data it is difficult to 
turn these figures into anything that might correlate with local differences 
in vegetation. The most important considerations that can be discussed with 
present knowledge are the relative shortness of the season for plant growth, 
