History of lake Agassis. — Ujpliam. 223 
These beaches are separated by vertical intervals that vary" from 
10 to 45 feet through the range of elevation between the lowest 
McCauleyville beach and lake Winnipeg, which was originally 
twenty feet higher than now. As soon as the ice upon Hudson 
and James bays and the adjoining country had so receded as to 
give to lake Agassiz an outlet lower than the river Warren, it 
began to be drained in that direction, perhaps flowing at first across 
the water-shed between the Poplar and Severn, and later along 
lower courses, including the canoe route by the Hill and Hayes 
rivers. Each of its successive outlets was probably eroded to a 
considerable depth, being occupied by the outflowing river during 
the time of formation of two or more beaches, until the retreat of 
the southeastern border of the portion of the ice-sheet remaining 
west of Hudson bay finally permitted drainage to take the course 
of the Nelson, the ice-dammed lake Agassiz being thus changed 
to lake Winnipeg. The northeastern outflow commenced when 
the lake at the latitude of the south end of lake Winnipeg stood 
about 1,000 feet above the present sea level, and it was gradually 
lowered to 730 feet when the Nelson between its successive lakes 
began to erode the shallow channel of the upper part of its course. 
Fossils have been found in the deposits of lake Agassiz at two 
localities. They are all fresh-water shells of species now livino- in 
this district, occurring in beach ridges where excavations have 
been made to obtain sand for masons' use. The Campbell beach 
about six miles southwest of Campbell, Minnesota, at an elevation 
approximately 985 feet above the sea, has thus yielded shells of 
Unio ellipsis Lea, a common species of the upper Mississippi re- 
gion. In the Gladstone beach, a half mile northeast of Gladstone 
Manitoba, about 875 feet above the sea and 165 feet above lake 
Winnipeg, four species occur in considerable abundance from two 
to four feet below the surface, namely, Unio luteolus Lamarck, 
Sphcerium striatinum Lam., Sphcerium sulcatum Lam., and Gy- 
raulns parvus Say. These species from both localities were 
kindly determined by Prof. R Ellsworth Call, who states that 
Unio luteolus is one of the most widely distributed representatives 
of the genus, its range being from Lake Winnipeg to Texas, east 
to New York, and west to Montana. It is generally abundant in 
Minnesota. Both these species of Sphcerium are reported by Dr. 
Dawson from the Lake of the Woods and Pembina river ; and the 
first is the most common species of its genus in Minnesota, while 
