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Brick and tile are manufactured from gray drift at Jackson, where 15 feet of yellow clay, with very little limestone or other impurities, extends over an area of 14 acres. The deposit is close to the Chicago, Milwaukee & St. Paul Railway, and conditions seem to be favorable for the development of a considerable industry. This plant has used the dry process of separating limestone from the clay. The pit is kept dry and the clay is plowed over a considerable surface and gathered up only after the wind and sun have dried it thoroughly. It is then transferred to sheds for further drying with protection from rain. The crushing is done in a modified dry pan, from which an elevator carries the clay to a screen. When pebbles accumulate in the dry pan it is stopped and cleaned out. Lack of shed room limits the capacity and output of the plant.
The nature of the gray drift of Jackson County is indicated by the following tests. The clay slakes in two minutes and is highly plastic, with 29 per cent of water. It shrinks 6 per cent on drying and develops a tensile strength of 125 pounds to the square inch. Burning tests gave the results set forth below:
| Cone No. | Color. | Shrinkage. | Absorption. |
| Per cent. | Per cent. | ||
| 04 | Salmon | 2 | 25 |
| 02 | Buff | 3 | 22 |
| 01 | …do | 5 | 14 |
| 1 | Greenish buff | 8 | 6 |
| 2 | …do | 10 | 1 |
The clay is too hard to scratch with a knife after burning to cone 02 (2,030° F.) and reaches viscosity at cone 2 (2,138° F.). If the
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limestone pebbles are not removed most of the burned products slake after exposure; if they are removed good brick are produced.
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