284 UXITED STATES GEOLOGICAL SURVEY— TERTIARY FLORA. 



TertiaiT formations, twentv-ono species, descriljcd citlior from leaflets only, 

 or from leaves and fruits I'oiiml together, or friim fniils alone; and, besides, 

 six species o^ Ptcrccarya. 



At tlie ]ireseiit time, one species only of Jiiglans is known. Its leaflets 

 liavc the borders entire. It is the noble J. regia, Linn., whicli, b\' cultiva- 

 tion in Middle and Southern Europe, has given numerous varieties, all bearing 

 fruits, known everywhere as palatable and nutritious food. In its wild state, 

 it inhabits the trans-Caucasian provinces of Asia. In the section of the 

 serrate leaflets, Juglnns has three well-known species: J. nigra, Linn., J. 

 cinerea, Linn., of the Eastern United States of North America, and J. rupestrh, 

 Engelm., indigenous in New Mexico; a fourth species, whose fruit resembles 

 that of the Butternut, is found in Asiatic Russia. In the genus Can/a, all the 

 living species, nine, belong also to the eastern slope of this continent. One 

 only, which is mentioned as not satisfactorily known, belongs to Mexico. 

 From this, it is evident that there is in Europe an anomaly of distribution in 

 con.sidering the numerous species tliere known from the Tertiary, while none 

 at all is left in the flora of that continent. In North America, species of 

 Jtiglans are already represented in the Kocene of Golden, Black Buttes, Spring 

 Canon, etc., mostly l)y leaflets with entire borders, more numerous still at 

 Evanston and in the Green River group. Of the section of dentate leaflets, 

 two species have been described from the Eocene of the Mississippi; none, 

 however, from that of the Rocky Mountains. They appear first in the 

 Evanston group, and continue in an increasing proportion upward, while those 

 of the other section l)ecome less preponderant, as evinced in the Pliocene of 

 California, where one species only of this last section is present, while it has 

 four distinct ones with denticulate or serrate leaflets. Tiiis seems like a 

 premonstration of the present character of our Jiigland'tneue, which all have 

 dentate or serrate leaflets, and of the future preponderance of their species. 



JUGLANS, Linn. 



§ \. — Leajlets entire. 



J (I g; I :t 11 s r !i a in II o i d o f^ , Lesqx. 



I'late LIV, Figs. C-9. 

 JugJanD rhamnuides, Losqx., Annual Kepoit, 1871, p. 'J!)4 ; 1873, pp. 382, 400, 402. 



Leaves oval, narrowed in a ciirvo or ronniled to tbc petiole, very entire; lateral nerves tliin, 

 distant, curved in passing to the borders, caniptodronio. 



The leaflets are apparently taper-pointed or acuminate, very variable in 

 size, like all those referred to this seel ion ; the lateral nerves averaging 40'^ of 



