176 The American Geologist. March, 1902 
burned product exhibits a much coarser grain and poorer qual- 
itv than the gray clay below leads the writer to conclude that 
the source of supply was actually different and that the main 
characters of the red zone are original and not to any consid- 
erable extent induced. If this conclusion is at all correct it is 
reasonable to conclude further that the chief source of supply 
for this deposit was the glacial debris brought from the north- 
west, that it was accompanied and succeeded by an invasion of 
red material from the east and. that its best development pre- 
ceded the withdrawal of the ice from this region. In short it 
was in a minor way inter-glacial as related to the oscillations of 
the Wisconsin stage of the Ice Age. Whether this deposit 
formed in “Lake Nemadji” of Professor Winchell’s writings _ 
or in some earlier one, is of little consequence in this general 
treatment. Certainly one other deposit further south along the 
St. Croix was accumulated earlier. 
3. Glacial Stream Deposits. In this type is included the 
river silts deposited during the withdrawal of the ice. During 
this time no doubt many of the streams were large and at times 
heavily laden with fine matter gathered from glacial debris. 
In occasional quiet eddies or other still water some of this load 
would surely be dropped. The result has been some very val- 
uable and accessible brick clays. There are two areas prom- 
inent in this state in such clays. One is along the present 
Minnesota river from Shakopee ‘to New Ulm and the other is 
along the Mississippi river from Minneapolis to Little Falls. 
In both cases the worked clays form a part of terraces bor- 
dering the present river channels. In some cases there may 
easily be a reasonable doubt as to the exact age of the deposits, 
but in the case of the chief representatives it seems certain that 
they were accumulated close upon the withdrawal of the ice 
borders. A few may be even interglacial. The source of ma- 
terial is all western drift and as a result the clays burn cream 
and gray. 
These clays occupy first rank in point of production. The 
most extensive plants are at Chaska in the Minnesota valley, 
and at Minneapolis in the Mississippi valley Both localities 
produce immense quantities of common brick of good quality 
and easy, cheap manufacture. The largest brick plant in Min- 
nesota is located at Chaska. 
