Minnesota Clays.—Berkey. 173 
2. Clay Shales Formations. Shales are sedimentary rocks 
formed as the direct result of transportation of residuary and 
decay products and their assortment by water. They are, as 
clay shales, fine grained, friable and carry varying quantities 
of such impurities as sand, lime, iron and organic matter. 
Such shales are abundant in the sedimentary districts of 
Minnesota. To this class belong some of the most valuable 
and noted deposits of the state. 
The Ordovician shales are found only in the southeastern 
- quarter of the state. Minneapolis is very near this northern 
limit. The Minnesota river bluffs near St. Paul exhibit their 
typical development and relationships to the limestone beds of 
the ordovician. Alternating beds of limestone and shales oc- 
cur with the result that an excess of lime renders a large por- 
tion of the total thickness unsuited to economic uses. But from 
these shales the Twin City Brick Company, whose plant is in 
St. Paul, make the only first-class brick produced at the present 
time in Minnesota. Grave difficulties to successful working 
-have been so far overcome by this company that they already 
have a reputation throughout a large part of the United States 
for an exceptionally attractive line, of front brick. Their 
range of artistic colors in pressed brick is the envy and de- 
spair of almost every competitor now in the market. 
Although the same beds occur in abundance at other points 
in the general district mentioned, and although they have 
proven so valuable to this one company, still no other develop- 
ment of them has yet been attempted. 
Cretaceous shales in at least one occurrence are very noted 
and of great value. This is in the case of the stoneware clay 
of Red Wing. The deposit there is very limited in area and 
bears some evidence of considerable glacial disturbance but it 
is essentially a representative of the great shales formations 
of Cretaceous age. Stoneware industries founded upon this 
deposit at Red Wing have no superiors in quality or quantity 
of product in the United States. 
Similar formations occur at other points especially in the 
western half of the state beneath the drift, but none have yet 
been found to exhibit so valuable qualities as the Red Wing 
stoneware clay. 
