314 MESOZOIC FLORAS OF UNITED STATES. 



In drawing conchisions as to the age of this flora we ma}' omit 

 Dicksonia montanensis, D. pachyphylla,'' Nageiopsis montanensis, Lycopo- 

 dites f montanensis, Cycadeospermum montanense as being new species 

 or too imperfect!}'' characterized. Cladophlebis constricta ? and Ceph- 

 alotaxopsis ramosa ? also should be omitted as being not determined 

 with positiveness. The remaining plants are not of equal value in 

 fixing the age. 



Equisetum Phillipsii, from its great abundance, has a high value. 

 As is known, this is a Wealden form. E. Lyellii also is Wealden, but 

 from its greater rarity and the possibility that it may be some portion 

 of E. Phillipsii it has not so much weight. The Cladophlebis falcata 

 montanensis is near enough to the Potomac form to be regarded as its 

 representative modified by differences of environment. The Lower 

 Potomac strata which contain the type form are shown by their flora 

 to be Wealden in age. Cladophlebis heterophylla is a plant of the Great 

 Falls beds, which have many forms in common with the Lower Potomac. 

 Thyrsopteris elliptica occurs in too few specimens to have much value, 

 as it can not, from the specimens, be regarded as a common and char- 

 acteristic plant of the Geyser beds, but it strengthens the resemblance 

 of this flora to that of the Lower Potomac. 



Nilsonia schaumburgensis is of high value in determining age. It is 

 an important and characteristic plant in the European Wealden flora, and 

 its great abundance in the Geyser strata shows that it is one of the most 

 characteristic for the Montana locality. Its occurrence there adds another, 

 and a most important, form to those that Yokoyama had previously made 

 known as common to the Lower Cretaceous flora of Japan and the United 

 States. Its presence in the Geyser flora strongly confirms the conclusion 

 that its age is Wealden. Zamites arcticus " also must be considered as one 

 of the most characteristic plants of these beds. This type of Zamites not 

 only indicates the Wealden age of the beds containing it but shows that 

 they have elements characteristic of the Kootanie and the Great Falls 

 formations. 



Laricopsis longifolia latifolia is so near the type plant of the Lower 

 Potomac that it may be regarded as its representative, and it gives 



« Professor Fontaine was not aware at the time'of preparing this report that this species occurred in the 

 Shasta formation. It is found only in the lower or Knoxrille member of that formation. — L. F. W. 

 f> This also occues in the Knoxville beds of the Shasta formation. — L. F. W. 



