350 UNITED STATES GEOLOGICAL SUllYEY— TERTIARY FLORA. 



biformis, and Sequoia longifolia^ imparts to it a more ancient physiognomy, 

 it is either as remnants of the past, merely recording a few features of old 

 generations passed away, or as contemporaneous, long-persistent types, which 

 do not distinctly characterize any peculiar epoch. As proof of this assertion, 

 we have the true Lower Eocene character marked in the same flora of Point 

 of Rocks by four species, Ficus planicostata, Vihurnum marginatum, Populus 

 viclanoroides, and Greiviopsis CIchurni, intimately related to species of the 

 Sezanne flora, and not at all or very ol)scurely to that of the Cretaceous. 



The flora of Point of Rocks is allied to that of Black Buttes by nine 

 identical forms, or by one-third of its species. In considering the evidence 

 of synchronism, the identity of two floras conld not be more jjositively proved 

 than this, and, nevertheless, we have here two to three thousand feet of 

 interposed measures. It is a remarkable fact, upon which more will be said 

 presently. The groups of plants at Point of Rocks has, besides the Eocene 

 representatives, six species identified with, and as many related to those of 

 the Miocene of Europe. Therefore, we see here, what has been remarked 

 in other localities of the Lignitic, a compound or admixture of old and young 

 Tertiary types, in comparison at least with the fossil floras of Europe, and 

 thus a general character which does not distinctly relate our first group to 

 any peculiar stage of tlie European Tertiary. We have the Paleocene by 

 relation to species of Gelinden and Sezanne; the Upper Eocene, especially 

 the Ligurian, or Oligocene, by the Palms; and the Miocene by a number of 

 'common and generally distributed forms, which, like Sequoia hrevifolia, 

 Sequoia Langsdorfii, Populus mutahilis, Ficus tiliafolla, Rhummis rectincrvis, 

 Juglavs /ugosa, etc., are persistent types of wide distribution, indicating 

 merely the Tertiary age for the Lignitic flora. For this reason, I shall con- 

 tinue to carefully record its points of affinity with the divers groups of the 

 geological floras of Europe; but at the same time, denying as yet sufficient 

 evidence for its identification to any of them, I persist in considering it sim- 

 ply as the Lower Eocene flora of this continent. 



I said above that the identity of specific forms at Point of Rocks and 

 Black Buttes is worth recording as a remarkable case in regard to the dis- 

 tribution of plants. In marine strata, the persistence of types is a matter 

 of little concern, for the circumstances under which the marine faunas and 

 floras are distributed, for example, the mineral elements entering into the 

 compounds, the depth and temperature of the water, etc., may continue the 



