The general lithologic character of the Paleozoic rocks of the Northern Mid-Continent region

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is compared and contrasted with that of the Rocky Mountain region. It is noted that Pennsylvanian and Permian rocks occur extensively below Jurassic sediments in the Denver basin with progressive changes from the typical lithologies of eastern Kansas and southeastern Nebraska to the significantly different lithologies of eastern Wyoming and southwestern South Dakota. The pre-Pennsylvanian Paleozoic rocks, however, have not been traced to date through the Denver basin between the outcrop areas southeast and northwest of the basin, and there is evidence of a broad, northeast-southwest band through the basin where Pennsylvanian rocks rest on the pre-Cambrian. It appears that the Mississippian rests on progressively older pre-Mississippian sediments as this area is approached. The Paleozo c history of the Denver basin, as interpreted from available data, is presented.

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