2g2 The America?! Geologist. May, i9oy 
Southward, also, large tracts of modified drift reach several 
miles to the southwest and south from Minneapolis; and they 
again occur in characteristic development, beyond a belt of 
morainic hills, upon a large part of Dakota county, in the 
angle between the Minnesota and the Lake Superior lobes of 
the ice-sheet, as they existed at the time when the great marg- 
inal moraines of the Wisconsin stage of glacial retreat began 
to be formed.* The modified drift in Minneapolis is thus seen 
to have owed its origin to drainage from the receding icefields, 
not to the Mississippi river. It is part of a belt of gravel and 
sand plains extending about 400 miles, progressively deposited 
as the ice boundaries withdrew from south to north. Within 
the Minneapolis area the deposition closely attended the gla- 
cial recession, taking place largely at the edge of the icefields, 
and reaching apparently only a few miles away; except that 
the greater part of the fine silt and clay, which could be borne 
in slowly flowing water, passed far down the Mississippi val- 
ley. 
Adjoining the south side of the Lowry hill esker, close 
northeast of the Lake of the Isles, a very gently sloping plain 
of modified drift reaches a quarter of a mile from the esker 
ridge, and has a descent in this distance from 920 or in part 
915 feet, at its upper edge abutting on the esker, to 910 feet. 
Next southward there is a more rapid descent of the sand sur- 
face, 20 to 25 feet; and thence a slightly undulating plain of 
the same gravel and sand, 890 to 875 feet above the sea level, 
stretches three miles south, adjoining the east side of the Lake 
of the Isles, and of lakes Calhoun and Harriet. This wide 
plain declines slowly eastward, or at some lines it has a rather 
abrupt general descent of 5 or 10 feet, to the height of about 
860 feet at the east end of this esker series and thence south 
to the vicinity of Powder Horn lake and nearly to the Wash- 
burn Memorial Orphans' Home. Thence to the east and 
southeast its inclination continues, sinking to about 830 or 825 
feet before reaching the Mississippi river. This stream was 
pushed to the east side of the modified drift plain by the east- 
ward slope, and it there trenched through the drift and its re- 
ceding waterfall cut a gorge about 100 feet deep in the Trenton 
♦Bulletin of the Minnesota Academy of Natural Sciences, vol. iii, pp. 
51-56. 
