Throughout most of the past century, the topographically high felsitic rocks of the St. Francois Mountains in southeastern Missouri have been interpreted as exhumed pre-Cambrian mountain peaks which had been buried beneath Cambrian and Ordovician sediments.

Prevalence in part of the region of sub-horizontal (contouring) felsite-Paleozoic contacts which define a regional, mildly undulating surface, truncation of Cambrian and Lower Ordovician formations by these felsites, and abundant evidence that such contacts are tectonic rather than depositional indicate that these topographically high felsites lie above the Paleozoic strata, and are in regional thrust relationship.

Among previously enigmatic, incongruous, or misinterpreted phenomena attributable to this tectonism are: (1) numerous klippen and other probable klippen composed almost entirely of pre-Cambrian igneous and metamorphic rocks; (2) northeasterly directed, shallow-rooted, compressional structure, including minor thrusting, in the autochthonous Paleozoic rocks; and (3) widespread brecciation, prolific silicification, lead-zinc, barite, and other mineralization, together with some alkaline-mafic intrusions. These associated phenomena involve surface-exposed strata from the Cambrian to the Permian, and occur in several areas including at least western Kentucky, southern Illinois, southern Missouri, northern Arkansas, northeastern Oklahoma, and eastern Kansas.

A granite-felsite complex of autochthonous pre-Cambrian is exposed in the northeastern (structurally higher) part of the St. Francois Mountains.

The "roots" of this great thrust (or thrusts) are most probably in the Ouachita geosynclinal belt of southern Arkansas and Oklahoma; the age of the thrusting appears to be latest Permian and(or) later--perhaps Appalachian.