ABSTRACT

The most outstanding structure around Glacier National Park is the Lewis thrust, which sharply separates the two main tectonic units of the region. Southwest of the Lewis thrust, Preacmbrian metasedimentary rocks are exposed in broad, open, northwest trending folds. Northeast of the Lewis thrust, Paleozoic carbonate rocks and Mesozoic shales are imbricated by numerous southwest-dipping thrusts.

The Clarke Range salient does not represent differential movement of the Lewis thrust plate, but the salient parallels the original configuration of the detached plate of strata.

The disturbed belt is subdivided into a western unit, in which Paleozoic rocks are involved in the thrusting--and an eastern unit, in which only the Mesozoic rocks are imbricated. The folds west of the Lewis thrust generally parallel the structures in the eastern part of the disturbed belt, but the western subdivision of the disturbed belt forms a large northeast-facing salient with a discordant north end.

A southeast-trending complex of normal faults parallels the North Fork of the Flathead River. The gross effect of these faults is a series of northeast-facing homoclines.