In a general way the state may be divided into three geologic zones. The first is an area where igneous and metamorphic rocks are exposed or occur beneath the unconsolidated mantle of glacial drift. This includes all of the northeastern part of the state and a considerable area in the central part and along the Minnesota river valley. Igneous rocks have solidified from a molten condition and metamorphic rocks have been formed from pre-existing igneous and sedimentary rocks by heat, pressure, and movement. It is to be expected that both of these classes of rocks would have a low porosity and, therefore, yield little water. Artesian water is, therefore, rare in these rocks of low porosity, although sometimes found in fracture zones or in the porous upper portions of lava flows. From the point of view of extensive artesian supplies we may eliminate this area from consideration. The second geologic zone is a series of areas in western Minnesota,2 where relatively thin deposits of Cretaceous sandstones and shales are found beneath the glacial drift and lying on the igneous and metamorphic rocks below. At places, especially near Marshall, the sand-