sentences:  The classification used below principally derives from Sansome's "Minnesota Underfoot - A Field Guide to Minnesota's Geology", but is also influenced by "Minnesota's Geology" by Ojakangas and Matsch.These authorities generally agree on areal borders, but the regions as defined by Ojakangas and Matsch are more geographical in their approximations of areas of similar geology, while Sansome's divisions are more irregular in shape in order to include within a region all areas of similar geology, with particular emphasis on the effects of recent glaciation.As glaciation and its residue has largely dictated regional surface geology and topography, Sansome's divisions are often coextensive with ecological provinces, sections, and subsections.