Minnesota Clays.—Berkey. 171 
ORIGIN AND DISTRIBUTION OF MINNESOTA* 
CLAYS. 
By CHARLES P. BerkKf&ty, Minneapolis. 
Minnesota is represented by the usual kinds of clays in fair 
abundance. In a natural classification based upon origin as the 
chief principle of separation all of the different members are 
to be found within her boundaries. But the rather common 
classification into brick clays, pottery clays, fire clays etc., is 
not serviceable in the present study of Minnesota material. + 
A wide range of uses has not yet been established with these 
materials, while the factors leading to definite conclusions as 
to origin are better known. 
The ultimate origin of all clays is the same the world 
over. Decay of feldspathic igneous rocks to earthy hydrous 
silicates has furnished practically all of the materials from 
which has been derived and accumulated all the minor classes 
and qualities of clays. But the immediate origin of any par- 
ticular deposit is always some special method of accumula- 
tion or transportation and is nearly always determinable. It 
is these minor differences of origin that serve as the best 
means of separation into characteristic classes or types, and 
it is often these same differences that have most influenced 
the quality as well as the abundance of neighboring deposits. 
The terms necessarily used in such a classification are well 
known to every student so that definitions are wholly unneces- 
sary, but a discussion of the development of the various clays 
of this state will give some opportunity to explain special 
features. 
I. Residuary Clays. 
These are clays of all sorts whose immediate origin is the 
decay of rock formations and in whose accumulation transpor- 
tation has not been a prominent factor. 
1. Kaolinic decay products from feldspathic rocks consti- 
tute the simplest case. Although rocks that would produce 
such materials are very abundant in Minnesota geological 
_* Abstract of a paper read before the Minnesota Academy of Natural 
Sciences, Peb 11, 1902. 
+ County descriptions in the series of Final Reports, vols. i, ii, and iv, of 
the Minnesota (seological and Natural History Survey contain many discus- 
os ot the clays of different localities in their relations to other geologic 
ormations. 
