
GLACIAL PHENOMENA AND SUPERFICIAL DEPOSITS. 257 
compares with high-level terraces, found on the hills west of Manitoba 
Lake, with an estimated height of 1,428 feet, and five hundred miles distant. 
We have therefore the most satisfactory evidence of the former depres- 
sion of the land to this extent in the eastern region, and it is difficult to 
understand by what waters it was covered, if not those of the sea. The 
correspondence in height of these terraces, and the plateau south of the 
Lake of the Wools, is remarkable. The height of Methy Portage— 
1,566 feet—which according to Sir J. Richardson’s description may be a 
similar drift plateau, with a northward-facing escarpment, also corres- 
ponds; and so, in a general way, does the average height of the Lauren- 
tian axis, and that of the southern part of the Coteau. Supposing the 
depression to have been everywhere equal, the water must at this time 
have reached to near the foot of the third prairie steppe, on the forty- 
ninth parallel. 
595. On passing up on to the higher levels of the prairie, we 
continue to find proof of the former action of the sea at yet greater 
elevations. On the summit of the third prairie steppe, with an average 
altitude of about 3,000 feet, debris of Laurentian and its flanking Silurian 
limestones is found over nearly the whole area; though now mingled 
with a preponderating quantity of Quartzite drift from the Rocky 
Mountains, and in many cases with a great proportion of softer material 
from the underlying rocks. The river valleys, and lower levels, fre- 
quently show true till or boulder-clay, while the summits of the plateaus 
are generally covered with shingly deposits, which may have been 
derived in part from the re-arrangement of boulder-clay, but appear to 
consist chiefly of beach material, like that of the flanks of the Rocky 
Mountains, and may have been carried here by small icebergs from the 
mountains themselves, or by shore ice. The larger icebergs, with Lau- 
rentian and Silurian limestone debris, must have drifted to the west or 
south-west with a prevailing current, bearing the moraine matter of 
glaciers; while the smaller bergs and floes of the Rocky Mountains, 
came generally eastward with prevalent winds or surface currents. It 
does not appear probable that they came directly eastward. They may 
have come from the south-east, borne by a superficial current mingling 
with adeep northern flow, in a manner analagous to the Arctic current 
and Gulf stream on the Newfoundland banks; or, perhaps even more 
probably, have floated from the north-west, or possibly from the north, 
touching here and there on their way on the shores of the Rocky 
Mountain land, 
17 D 
