The Ordovician formations of the Rocky Mountain region exhibit a remarkable unity in their stratigraphic development. A formational terminology in one area serves equally well in other areas, so that the most thoroughly documented stratigraphic relationships, such as those of the Bighorn and Winnipeg Formations, can be adopted as standards for the entire Rocky Mountain province. In explanation of this procedure, regional lithological similarities within formations and lithological contrasts between each formation are illustrated to show their relation to superpositionally significant unconformities. Existing zone and stage designations not based on adequate stratigraphic integration conflict with this scheme. The Bighorn cannot be entirely Richmondian, nor can the Winnipe be Trentonian to Chazyan if the superpositional aspect of stratigraphy is admitted as evidence for their derivation.

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