At Monticello, brick were made some years ago from a very sandy clay in the banks of the Mississippi River which is probably alluvium. The deposit seems to contain less than 20 per cent of clay substance, and yields a common red brick of poor quality. (Clays and Shales of Minnesota, Frank F. Grout and E. K. Soper, The University of Minnesota, Minneapolis, Minnesota, 1914, Page 172)