28 The American Geologist. juiy, i89i 
mon occurrence and are more or less constantl}' broken b}- the 
waves. When the Manitoba lol^e retired to the north and east of 
tlie country now partialh- occupied b}- lakes Manitolia and Win- 
uipegosis leaving ])Oulders thickly- scattered over the surface, the 
water stood at least eight}' or ninety' feet above the present level 
of lake Winnipegosis, but it does not appear to have stood at this 
height for any great length of time, since, in the northern portion 
of the region especiall}-, little or no alluvium has been deposited 
over the till and paleozoic rocks. In receding from this hight 
the water has left two moderateh* well marked beaches, that 
fifteen or twenty feet above lake Winnipegosis being possibly rep- 
resented farther south by the Ossowa beach, and northeast by 
the highest beach at the Grand Rapids. During this and the 
succeeding period when the waters stood at the level of the triple 
beach at Grand Eapids, from 80 to 05 feet above lake Winnipeg, 
the ice foot appears to have extended down the middle of lake 
Winnii3eg, and it was towards the end of this latter period that 
the moraine was formed across the summit of Black island. 
The ice then receded to the higher land east of lake Winnipeg, and 
there is no farther necessity for assuming an ice-barrier in that 
direction. 
The next time that the water came to a standstill it would 
seem to have been about forty feet above the present level of the 
lake, and the channel of drainage was probably through a wide 
valley- extending northward from Limestone ba}-. 
It was during this last recession that the smooth glaciated sur- 
face of the archien gneiss and schists on the eastern side of the 
Winnipeg basin was strewn with boulders fallen from the face of 
the glacier, and when the glacier had retired these lioulders were 
covered bj- and iniliedded in a soft blue clav, in which have since 
been formed many thin disc-like calcareous concretions. This clav 
doubtless consists of the finer material brought down b}- the gla- 
cier, and spi'ead over the adjoining lake floor l\v the action of 
the water. As far as seen, it ever3where lies on the smooth gla- 
ciated surface of the Archaean gneiss and schist, and is not under- 
lain l)y till. 
From the above considerations, which have l)cen very l)riefly 
stated, it would apjtear probable that lake Agassiz was not at any 
time of very vast extent. Init rather that it was a margin of water 
of \arving width lying along the face of a great glacier which 
was retiring down a graduall}- declining plain. 
