245 



Miocene : among others, a Cinnamomum, a Ficus, a Sniilax, and a Ehani- 

 nus; the last two represented by large leaves. It unites, therefore, in 

 its characters, Miocene Arctic types with Miocene types of Middle 

 Europe, and a few of those of the Lower American Lignitic, considered as 

 subtropical. This reunion of types at the same point indicates the wide 

 extent of the thermal zones during the Miocene period, as well as the 

 concordance of the floras with synchronous Miocene formations over 

 wide areas, even under distant degrees of latitude. It therefore dis- 

 proves the idea of a succession in time of formations bearing identical 

 characters so far as their fossil remains are concerned, and thus com- 

 plicates, at least for this country, tbe question of the migration of spe- 

 cies and of their derivation from a particular point. 



The flora of the Carbon group has some of its species scarely different 

 from species of our present flora, which may be considered as their ofl"- 

 spring. Populus latior is represented now by P. canadensis, P. monilifera, 

 P. angulata, three closely-allied species as variable and difficult to fix in 

 their characters as is the Miocene species. The Xorth American species 

 of Corylus are scarcely distinguishable from C. Macquarryi, very abund- 

 ant in the Miocene of Alaska and Greenland. Oar Platanus occidentalis 

 is a mere modification of P. aceroides, as both Acer saccharinum and 

 Acer dasycarpum are traceable with the same degree of evidence to Acer 

 trilohatum. A number of leaves are referable to a species of Asimina, sim- 

 ilar in form and nervation to those of our Papaw ; being, however, smaller. 

 In the Conifers, we have, at Carbon, Sequoia Langsdorfii^ closely allied to 

 S. sempervirens, the most common arborescent species of California, and 

 Taxodium duhium, with which T. distychum, the bald Cypress of the 

 southern swamps, is apparently identical. 



The fourth group, referred to the Upper Miocene, is distinct from the 

 Upper Lignitic, which it overlies in patches of moderate extent. It is a 

 fresh-water formation, mostly of laminated calcareous clay-shale, more or 

 less impregnated with bitumen, the result apparently of the periodical 

 drainage of shallow lakes and swamps. In places, tfiis shale holds a pro- 

 fusion of vegetable fragments, especially representing Conifers, with 

 insects, feathers, and scales of fishes. At some other localities it has no 

 plants whatever, but instead skeletons of small fishes in equal abundance. 

 The flora of this group is related to that of the European Miocene in a less 

 degree than the former. By its types, and essentially by its facies, it is 

 more closely allied to that of ISTorth America at the present time. Its 

 Conifers are referable to the genera Taxodium in two species. Sequoia in 

 three: Thuga, Glyptostrobus, Pinus, and Abies. It has also a number of 

 species of Myrica and Salix closely allied to living species ; and an 

 Ampelopsis, a Stapliylea, species of Ulonus, Planer a, Ilex, Juglans, etc., 

 all specifically related to recent types. From the preponderance of Coni- 

 fers and shrubs,the climate of this epoch appears to have been somewhat 

 colder than at the former period. 



In considering the distribution of the plants in the whole Tertiary of 

 the Rocky Mountains, there is evidence of a slow upheaval of the land, 

 of a comparative diminution of atmospheric humidity, and consequently 

 of a lowering of the temperature. During the process of formation of 

 this fourth group, the ground had become hilly, if not already mount- 

 ainous or subalpine ; the laud was a succession of valleys, hills, and 

 lakes ; the uplands covered with forests of Conifers, the swamps and 

 the dales with shrubs, willows, wax-myrtles, numerous species of holly, 

 sumac, etc. The Lignitic precedes in its formation the upheaval of the 

 mountains, while the strata of the Green River group were deposited 

 during the period of upheaval. The flora of the fourth group, known 



