Fossil plants support the hypothesis that an unconformity in the basal part of the Kootenai formation in Montana as it has been generally defined in the literature, and at the base of the lower Blairmore formation in Canada, marks the Jurassic-Cretaceous boundary. Comparison of the floras on both sides of the unconformity heightens the probability that the part of the Kootenai below the unconformity is to be included in the Morrison formation, which then is most likely equivalent in whole or large part to the Kootenay of Canada; and that the upper part of the Kootenai of the United States corresponds in large part with the lower Blairmore of Canada. The flora of the upper part of the Kootenai and of the lower Blairmore is an accepted Lower Cretaceous flora that contains s veral characteristic species not yet reported from any strata below the unconformity, or indeed, from any Jurassic strata.