826 The American GeoloyLsf. November, 1897 
extended northward with the departure of the ice sheet. This 
evidence consists not only in the occurrence of morainic belts in the 
basin occupied by the lake, but also in the absence of the upper beach 
in the northern latitVides. The upper or Herman beach can be traced 
on the west side of lake Agassiz from the outlet northward to the north 
part of the Pembina escarpment, a few miles north of the international 
boundary, but has not been found farther north. During the time oc- 
cupied in the formation of the Herman beach four moraines were 
formed and the ice border withdrew about 150 miles in Minnesota and 
150 to 200 miles in North Dakota and southern Manitoba. Mr. Upham 
thinks it probable that the border withdrew not less than 300 miles in 
the Red River valley, where lake Agassiz produced a more rapid break- 
ing down of the ice margin than on the neighboring land surfaces. At 
the close of this stage of the lake the outlet had been cut down at least 
25 feet and possibly 50 feet but this erosion was entirely in glacial de- 
posits. 
At the close of the Herman stage the lake probably had an area of 
about 26,000 square miles but it is thought to have subsequently ex- 
panded to at least 100,000 square miles or about the combined area of 
Wisconsin and Illinois and considerably more than the combined area 
of the Ave great Laurentian lakes. Before northeastward outlets be- 
gan to drain lake Agassiz the border of the ice sheet had probably been 
melted back from the present lake Winnepeg far toward Hudson bay 
and the outlet at the south had been cut down to a depth of about 90 
feet below the level of the Herman beach. With the uncovering of the 
Nelson river, lake Agassiz ceased to be held by the ice barrier and be- 
came lake Winnepeg. 
In the south part of the area of lake Agassiz five principal beaches 
have been observed and named from towns in Minnesota near which 
they are well exhibited, the Herman, Norcross, Tintah, Campbell and 
McCauleyville beaches. These beaches separate into distinct beachlets 
when traced north into Manitoba, there being seven beachlets corres- 
ponding to the single Herman beach at the southern outlet, two beach- 
lets each for the Norcross and Tintah, and three each for the Campbell 
and McCauleyville beaches. After the lake obtained its earliest out- 
let to the northeast it formed fourteen shore lines. There are thus 
thirty-one separate shore lines in the northern portion of this lake area 
and nearly all extend south of the international boundary. The 
changes in level during the period of southward discharge are due 
principally to differential northward uplift, only a small element of 
change being due to lowering of lake level by erosion of its outlet. The 
author estimates that there was a slight uplift of the outlet amounting 
possibly to 90 feet but perhaps not exceeding 50 feet. The north part 
of the basin was uplifted 200 to 300 feet or more, the amount becoming 
greater from south to, north. The beaches on the eastern shore are 
uplifted more than those on the western and the ratio of the eastward 
ascent to the greater northward ascent indicates that the uplift was 
from south-southwest to north-northeast. The changes of levels were 
