The solution to the problem of the mechanical origins of basins and troughs requires the recognition of the occurrences of crustal buckling, by lateral compression; crustal sagging, by loss of vertical support; and crustal thinning, by lateral tension. For this purpose recognition criteria have been developed. The most diagnostic are cited here.

FOR BUCKLING

During sedimentation:
There is practically no normal faulting; a negative isostatic gravity anomaly is developed.

After sedimentation:
The basin structure is inverted to a dome by central uplift of about 1/3 the stratigraphic depth.

FOR SAGGING

During sedimentation:
There is considerable normal faulting with small or cancelling heaves.

After sedimentation:
There is no local movement and the basin is permanent.

FOR THINNING

During sedimentation:
There is normal faulting with large heave components and the crustal layers are thinned appreciably.

After sedimentation:
There is slight inversion of the basin structure to a dome by central uplift of about 1/11th of the stratigraphic depth.

These criteria are simply an advanced statement of uniformitarianism. Continuity is given to these actions by a development of the concept that regional geologic history occurs in a closed mechanical system. In this system displaced, eroded, and deposited volumes are accountable. An illustration of the analysis is given with the tentative conclusion that the Ardmore-Marietta basin structure of Oklahoma and Texas could not be the result of crustal buckling during deposition. The purpose of the paper is to clarify the pragmatic principles basic to tectonic theory.