38 



LAMINATED CLAYS OF GRANTSBURG, WIS. 



however, is prominent enough to overcome their effects, so that the 

 burned wares are all red. 



Where successive laminae are so divergent in characters, it is 

 evident that there might be considerable difference in chemical 

 analysis from different samples. For ordinary brick-making pur- 

 poses the material is mixed as thoroughly as possible with the equip- 

 ment of the plant. Such a mixture would best represent the com- 

 position of the deposit as a whole. Nearly all the work yet done has 

 been upon the upper zone of about 15 feet. Two samples out of 

 this zone give the following results in a partial analysis. No. I is 

 mixed material and fairly representative. No. II is from the upper- 

 most layers. 



This leaves a balance of 2.04 and 0.83 per cent., respectively, for 

 the undetermined constituents. 



Economic value. — With moderately thorough mixing the Grants- 

 burg laminated clays make common stiff mud brick of excellent 

 quality. The fineness of grain and plasticity aid in producing an 

 unusually smooth finish. With hard burning the product is remark- 

 ably strong. The colors are all classed as red, but exhibit consider- 

 able range of shades, the hardest-burned lots being darkest in color. 

 Likewise the more exposed margins have darker color, so that sys- 

 tematic setting of the kiln with this result in view produces a varie- 

 gated ware that is considered attractive. 



All wares require a temperature of about 2,000° F. in burning. 

 The upper beds of Clam River are too sandy for use as clays at all. 

 At all other points, however, with careful mixing the material is 

 valuable for clay wares. Vitrified bricks have been made by the 

 company now operating at Grantsburg which seem to duplicate the 



