Page:The Journal of geology (IA journalofgeology21894univers).pdf/390

cates an age certainly Cretaceous, and probably middle Cretaceous."

Here, then, is an example of the value of a few fossil plants in determining the age of a series of beds where a hundred years of study from the stratigraphic side had failed to accomplish conclusive results.

The flora of the so-called Laramie beds of the Rocky Mountain region has also been the subject of much discussion and controversy. By certain of the older writers it was referred to the Tertiary, by others to the Upper Cretaceous. Recent investigation has shown, however, that several distinct horizons were embraced in what has been known as the Laramie. The tendency appears to be to restrict the term "Laramie," at least in the Colorado district, to the lower or older beds, and accordingly the Post Laramie beds have been differentiated and given independent names. As fossil plants are the most abundant organic remains present in this series of strata, their bearing on the question of the age and differentiation of the beds is important. No dependence can be placed on the earlier determinations of the distribution of the plants, for the reason that the different horizons had not then been distinguished, and the plants are often recorded from a locality at which several of the horizons are present and plant-bearing. It has been necessary to go over all the original material and determine by studying the matrix, and by duplicate collections, the actual horizon to which they belong. In this wat the status of 285 species now known to occur in these beds has been settled. In Colorado and New Mexico, the only area in which the interrelations have yet been worked out, it appears that there is a flora of 165 species, of which number 62 belong to the true Laramie and 103 to the Denver beds, and with only 7 species common to both. This proves beyond question that the Laramie and Denver beds are distinct, and that they possess, in certain clearly defined species of fossil plants, readily recognizable stratigraphic marks.

The deductions made from this datum point, viz.: the thorough study of the flora of the Colorado Laramie and allied