At Collegeville brick were burned for local use in the St. John's College buildings from a small deposit of yellowish laminated clay, which is apparently surrounded by coarse gravelly drift. It may be a fragment of some larger deposit, which was caught up by the last ice sheet and deposited in the midst of a gravelly moraine. The exposure sampled contains a number of limy concretions, but the brick that have been made do not seem to be damaged by them. Though too small and inaccessible to be of much interest, the clay was tested. It shows fair plasticity with 19 per cent of water. The shrinkage on drying is 3 per cent, and the tensile strength is 110 pounds to the square inch. Burning tests resulted as follows:
| Cone No. | Color. | Shrinkage | Absorption. |
| Per cent | Per cent | ||
| 05 | Salmon | 0 | 20 |
| 02 | Red | 2 | 16 |
| 01 | …do | 4 | 13 |
| 2 | …do | 6 | 9 |
| 3 | …do | 7 | 2 |
The clay is hard after burning to cone 02 (2,030° F.) and reaches viscosity at about cone 03 (2,174° F.).
Source:
Clay and Shales of Minnesota
Frank F. Grout with contributions by E. K. Soper
United States Geological Survey
Government Printing Office, Washington, D.C., 1919
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