374 THE JOURNAL OF GEOLOGY. 



cates an age certainly Cretaceous, and probably middle Cre- 

 taceous." 



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 Moun- 

 tain 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 investi- 

 gation has shown, however, that several distinct horizons were 

 embraced in what has been known as the Laramie. The tend- 

 ency 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 inde- 

 pendent names. As fossil plants are the most abundant organic 

 remains present in this series of strata, their bearing on the ques- 

 tion of the age and differentiation of the beds is important. No 

 dependence can be placed on the earlier determinations of the dis- 

 tribution 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 

 way 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 recogniz- 

 able stratigraphic marks. 



The deductions made from this datum point, viz. : the 

 thorough study of the flora of the Colorado Laramie and allied 



