Drift in Minneapolis, Mi?in. — Upham. 283 
Relations of the Northeastern and Northwestern Drift. 
To give a vivid impression of the complexity of the over- 
lapping and variously interstratified and mingled till or boul- 
der-clay deposits and associated modified drift of this area, I 
cannot do better than to quote from Prof. N. H. Winchell in 
his final report on Hennepin county, as follows: 
The origination and transport of the two tills may be considered prac- 
tically contemporary, as a totality, and due to the same general agent. 
Moreover, the gray till is not always found overlying the red. The two 
sometimes are mingled, and their color and composition, so far as they 
are characteristic of either, are lost. Sometimes several thin beds of 
gray till, somewhat modified by water, are seen to alternate with as many 
of the red. Sometimes patches of the gray are thrust over on to the gen- 
eral area of the red, isolated from the main mass of the gray Rut 
a single instance is known of the gray till underlying the red. 
Professor Winchell figures seven sections of the drift in 
Minneapolis, one being wholly modified drift. In the six sec- 
tions showing till, its predominant or only deposits are red, 
brought from the northeast, overlain by modified drift, or, in 
two places, by yellowish and gray till. In two places, red sand 
and gravel, lying next above the red till, are succeeded higher 
in the section by yellowish till, this color being due to a change 
from its original gray by peroxidation of its iron ingredient. 
The reddish till and modified drift owe their color to the 
fully oxidized iron of the red shales and sandstones of the 
Potsdam and Keweenawan formations in the region of lake 
Superior, which largely contributed, under glacial erosion, to 
the northeastern drift sheet. The boulders and gravel of this 
drift represent both the sedimentary and igneous rocks of 
northern Wisconsin and northeastern Minnesota ; but they in- 
clude no limestone, this rock being absent from the country 
whence the red drift was derived. In Minneapolis, however, 
occasionally blocks of limestone, derived from the northwest, 
are found in the red till, betokening some englacial intermix- 
ture of the two kinds of drift along the belt of confluent ice 
currents. 
The gray till, bluish at considerable depths, but weathered 
yellowish near the surface, contains a large proportion of clay 
and usually some small gravel of shale from erosion of Creta- 
ceous shales, and man}- boulders and smaller fragments of 
