390 GEOLOGICAL SUEVEY OF THE TEERITOEIES. 



Pterocarya americana, sp. nov. — M. P. 

 Gary a Heerii(l), Ett.— Gr. R. 

 Podogonium, fruit. — M. P. 

 Podogonium, leaf. — S. P. 

 C8esalpinia("?) linearifolia, sp. nov. — S. P. 

 Acacia septentrionalis, sp. nov. — S. P. 

 Leguminosites, fruit and leaf. — El. 

 Carpolithes et semina. — M. P. 



EEMARKS ON THE SPECIES OF THE FOURTH GROUP. 



The fourth group is remarkably distinct from the lower ones by its 

 peculiar /acies. It has for characters of its flora a proportionally large 

 number of ferns, 6 species, a Salvinia, a Lycopodium, 2 species of 

 Equisetum^ 11 species of conifers, and 9 species of Glumacece, viz : 

 30 species of acrogenous monocotyledonous and gymnospermous plants, 

 or 37 per cent, of the whole number of species as yet known 

 as its representatives. Moreover, the balance of the species is limited 

 to few genera : to Salix^ 3 species ; Myrica and Comptonia, 7 ; Quer- 

 cus, 5; Ilex, 4 ; Rhus, 2 ; Juglandece, 6. At first sight, this group appears 

 scarcely referable to a Miocene flora, so different is its fades from 

 that of any of the former divisions. It has, however, 32 of its 

 species identical with species of the European Miocene, or a propor- 

 tion of 40 per cent. ; while it is allied only to the lowest American group 

 l)y 5 species, mostly of general distribution : Pteris pennceformis, 

 Phragmites (Eningensis, Fagus feronice, Juglans ScJiimperi. With the 

 second group it has in common the same Phragmites, Salix angusta, 

 Ginnamomuni Seheuehzeri and Juglans denticulata / and with the third 

 Phragmites still, Equisetum Haydenii, Taxodium duhium, Ficus lanceo- 

 lata, Juglans acuminata, and J. denticulata. It has thus preserved a 

 remnant of the flora of the other groups, which, considered altogether, is 

 very little ; for the three first divisions have 267 species, and in elim- 

 inating Phragmites (Eningensis, represented in all the divisions of the 

 Tertiary, we find only 11 species, or 5 per cent., of the flora of the 

 Green Eiver group represented in the others. If it had not so many 

 typical representatives of the Miocene of Europe, and if at the same time 

 it had some one of our living species, it might be considered as Pliocene. 

 But of more recent types than those of the former groups, it has scarcely 

 any ; I can name only Ulmus tenuinervis, the fine Staphylea acuminata, 

 and Ampelopsis tertiaria. The remains of plants at Green Eiver are 

 found in laminated shales with an abundance of skeletons of fishes. At 

 Elko station, South and Middle Parks, the plant-bearing beds, com- 

 posed of the same kind of thin, laminated, fragile, soft shale, have also 

 preserved remains of fishes, insects, and feathers. 



The peculiar compound of the thin laminated slates of the formation, 

 and the similarity of animal fossil remains, prove, as well as the gen- 

 eral character of the flora, that the localities named in the above table 

 are referable to the same group. Very few species, however, have been 

 observed at more than one locality ; while, on the contrary, the species, 

 most of them at least, are represented by a very large number of speci- 

 mens. This fact, like the distribution of the species, indicates a vege- 

 tation of high land, covered with lakes, swamps, and deep forests ot 

 conifers, with a thick undergrowth of ferns and shrubs. With a 

 vegetation of this kind, the number of species is limited, and these are 

 generally circumscribed in local groups. A vegetation analogous to 

 this, covered the northern half of Europe after the Drift period. In the 

 Tertiary epoch it has its analogue with the (Euingen or upper stage of 

 the Miocene. 



