THE AGE OF TOE LIGNITIO FORMATION BY ITS FAUNA. 31 



own observations when I explored the range, I found it near Salt Wells, 

 or below Point of Rocks. If, then, we find the fossil flora of this last 

 locality agreeing in characters with that of Black Butte, if this one bears the 

 same degree of relation to that of the Colorado Basin, and to that of the 

 North Lignitic or of the Fort Union group, we shall have to conclude that 

 these land formations of the great Lignilic are contemporaneous, and the 

 question of their age has to be decided, I think, hy the comparison of the 

 vegetable types represented in the whole Lignitic formation. This can be 

 done only after the description of the species and the exposition of their 

 characters. 



