The post-Sauk Paleozoic of the U.S. and at least southern Canada, except incompletely interpreted late Paleozoic in the Cordilleran and Ouachita regions, comprises 6 major discontinuity-bounded sequences. In addition to 2 previously defined by Sloss et al., (Tippecanoe and modified Absaroka), 4 others include: 2 sequences separated by the Taconic discontinuity and confined to the eastern craton and Appalachian geosyncline, but together occupying the Tippecanoe interval; and 2 virtually transcontinental sequences, separated by the Acadian discontinuity, and together comprising approximate "Kaskaskia" interval of Sloss et al. The discontinuities are: I, unnamed pre-Tippecanoe (pre-"Chazy-Black River"); II, Taconic, pre-Silurian (eastern America only); III, unnamed pre-"mid"-Devonian; IV, Acadian, pre-latest Devonian; and V, unnamed pre-Absaroka (about pre-Des Moines). I, II, and V have been widely recognized; III has been appreciated regionally in the Rocky Mountains and Great Plains of northern U.S. and southern Canada, but otherwise previously envisaged rather locally; and IV, long recognized in Maritime Provinces and New England, and also shown from southern Appalachians to Oklahoma, but otherwise previously demonstrated in many widely scattered areas. These sequences and their many interregional stratigraphic "constants, " together with the intervening lacunas and their deformation-erosion differentials, demonstrate a striking historical episodicity which is unrelated to and obscured by the arbitrary time-stratigraphic subdivisions (systems, etc.) of the stratal record. Moreover, both physical and biostratigraphic patterns comprise a mutually harmonious and relatively simple order, which, by implication, tends to negate most of the previously envisaged persistent positive and negative intracratonic tectonic features.

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