Cambrian volcanics and Precambrian basement rocks produced an irregular topography in the Mid-Continent during intermittent Late Cambrian-Early Ordovician inundations. Large islands remained until Roubidouxian time; highest peaks persisted until Mississippian. The early Paleozoic sequence in thickest in inter-island channels of northeastern Oklahoma and in the more rapidly and uniformly subsiding basinal areas of southern Oklahoma.

Dresbachian transgression, spreading west, north, and possibly south, failed to reach most of Kansas and northern Oklahoma. During Ranconian time, only southern Oklahoma and mIssouri received sediments; Trempealeauan inundation covered all but central Kansas and the islands of northeastern Oklahoma. Sandstone and carbonate comprise the Cambrian.

Following post-Cambrian regression, Ordovician seas spread a blanket of carbonate over most of Oklahoma and Kansas. Sandstone is most abundant at the base of the Gasconade in eastern Oklahoma. It is also common in Roubidouxian rocks.

Paleogeographic maps and a worm's eye map illustrate the intermittent nature of the transgressions and emphasize the inherent problems of time correlation.

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