194 The American Geologist. Marcii, i89i 
in the northern part of the explored area of lake Agassiz this 
upper or Herman beach, which is single along the southern part of 
the lake, becomes divided into numerous parallel beaches that were 
formed at intervals of pause in a progressive elevation of that 
area. A portion of these relative changes of level, however, was 
due to a subsidence of the lake itself toward the north, on account 
of the diminution of its attraction by gravitation toward the ice- 
sheet, proportionate with the decrease of the ice in its final melt- 
ing. As many as six other Herman stages below the highest are 
recognizable by beach deposits, which indicate a rise of the land 
combined with a sinking of the lake to the amount successively of 
about 8, 10, 7, 15, 10, and 5 feet, or in total of 55 feet, on the line 
between North Dakota and Manitoba, while } r et the relative eleva- 
tions of the lake and the adjoining land along its southern part for 
some seventy-five miles northward from lake Traverse remained 
with only slight changes, not sufficient for the formation of any 
secondary beach ridge. 
In a later part of this report the discussion of the causes of 
these changes in the night of the land and of the lake is accom- 
panied by a table of the present elevations of the successive 
beaches formed by the lake on its west side through its entire ex- 
istence, until it was drained to the levels of lakes Manitoba and 
"Winnipeg. The two highest beaches (« and aa) in the Herman 
series of this table were not found north of the Pembina Mountain 
escarpment ; but the next two (b and bb) are well developed at 
Brandon and near Neepawa, reaching thus to the northern limit of 
my exploration at the south end of Riding mountain. During the 
interval between these Herman beaches a and b, the combined rise 
of the land and fall of the lake were only eighteen or twenty feet 
on the international boundary ; but in this time the southern end 
of the ice-lobe west of the lake had been withdrawn from the east 
part of the Tiger hills to Riding mountain, and the Assiniboine 
delta was being rapidl} T deposited. The northward extent of lake 
Agassiz in its subsequent Herman stages is not definitely deter- 
mined, but evidently some of the upper beaches observed by Mr. 
Tyrrell on the foot slopes east of the escarpments of Riding and 
Duck mountains belong to this series, the highest, according to in- 
formation supplied by him, being in lat. 51° 52' or two hundred 
miles north of the international boundary, at an elevation of about 
1,460 feet above the sea. 
