Water-Table of the Loess

McGee, Calvin, Bain, Todd, and other Iowa geologists, repeatedly direct attention to the occurrence of an iron streak in many loess sections. No offer is made of an explanation of its possible origin. In recent, extensive, street-grading operations in Des Moines, clue is given to this phenomenon. It does not reveal itself usually in small exposures or in building excavations. But in long hill-side grades it is found to be the line of the old water-table, the level of phreatic waters, and, as shown by filled-up wells of the early settlers, to be the depth to which they had to dig in order to obtain their permanent water supplies for domestic purposes. In a hill-side cutting passing through two till-sheets separated from each other by loess bed 20 feet thick, the iron-streak follows the contour of the sloping ground-surface, about 12 feet down, and thus cuts diagonally across all three deposits. This limonite streak appears to be clue to the oxidation of the iron carbonate in the ground-waters at the surface of the latter. In places these ground-waters appear to have oscillated considerably, and in the loess to give rise to phenomenon of stratified loess