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A plant was operated about a mile south of Belle Plaine on a bank whose structure is shown in figure 37 [below]. The different parts of the
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bank are not regular in their stratification, but the bedded clay exposed forms a sort of arch about 100 yards across. Each part of the section grades into the overlying and underlying parts. The yellow silt can be used as sand in tempering the lower clay. The clay slakes at once, requires only 21 per cent of water for molding, and is never very plastic. Soft-mud brick are to be made from it. The shrinkage on drying is 2 per cent, and the tensile strength less than 100 pounds to the square inch. Burning tests resulted as follows:
| Cone No. | Color. | Shrinkage | Absorption. |
| Per cent | Per cent | ||
| 02 | Cream | 0 | 35 |
| 01 | Buff | 0 | 33 |
| 1 | …do | 1 | 33 |
| 4 | …do | 2 | 28 |
| 6 | …do | 3 | … |
The clay is hard after burning to cone 01 (2,066° F.) and reaches viscosity at cone 6 (2,282° F.). The plant can produce about 30,000 soft-mud cream-colored brick a day.
Source:
Clays and Shales of Minnesota
Frank F. Grout with contributions by E. K. Soper
United States Geological Survey
Government Printing Office, Washington, D.C., 1919