Minnesota Clays.—Berkey. 177 
C. Recent Alluvial Deposits. The recent river muds are 
so closely related to the last class that in many cases it is not 
practicable to separate them. They occupy the same areas and 
are due to similar immediate conditions except the overwash 
source of material. 
D. Loess or Wind Deposits. To this class belong more of 
the clays usually worked on a small scale than to any other 
single one. Many are no doubt not true loess accumulations, 
but I have intended to include here all those in which wind 
transportation has been one of the chief factors in origin. 
Many of the ‘‘loams” reported from numerous localities really 
belong in this class. Some are described usually as “‘loess 
loams” and many might be called ‘“‘residuary loess.” Those in 
certain areas sometimes grade into one or another of the above — 
mentioned types especially the “glacial lake” and “residuary 
clays.” 
The loess clays with this interpretation are. therefore widely 
distributed although they are nowhere of very great thickness 
or of very special value. 
To this class the Red River valley clays which are of con- 
siderable local value in the vicinity of Moorhead and East 
Grand Forks seem to belong. In that district the workable 
stratum is only from six to twenty-four inches thick and lies 
immediately below the black soil and upon the sediments of 
glacial lake Agassiz. Southeastern Minnesota, especially the 
driftless area, also exhibits much loess-covered territory. 
Many small producers in widely scattered localities are work- 
ing this kind of clay. 
Summary. This article is intended to group the facts 
known as to the origin of Minnesota clays and point out typ- 
ical representatives of each geologic class. Although several 
of these different classes of material. overlap in occasional 
localities, in the main the distinctions are readily made out and 
the classification easy of application. 
The large clay working establishments of the state are us- 
ing either clay shales or stream deposits or glacial lake clays. 
The smaller and scattered brick plants of chiefly local import- 
ance are using fi// and modified drift or residuery loess and 
“loam” clays. 
