16f) UNITED STATES GEOLOGICAL SURVEY— TERTIARY FLORA. 



He adds : — "That some species ate also indicated in the Eocene, but they are 

 as uncertain as those of the Cretaceous, and it is only with the first deposits 

 of the Miocene epoch that every kind of doubt is put aside on this question, 

 for then we have not only numerous leaves of which the generic assimilation 

 is indubitable, but also flowers and fruits, which give to the botanists the 

 possibility of determining the subdivisions which had some representatives 

 at that time." It is certain that, according to the remarks of the same author, 

 it is during the Miocene period that the Willows have attained their maximum 

 of speci6c evolutions. But this extraordinary development of the generic 

 type is sufficient to prove the great antiquity of the genus, if even the pres- 

 ence of numerous leaves, as positively identifiable as those of the Miocene, 

 had not been found in the Cretaceous of both continents. To this we have to 

 add the continuity of the records from the Cretaceous through the Eocene and 

 the Oligocene. Schimper describes fifty-seven fossil species of Willows, two 

 of which are of doubtful generic relation. Adding to this S. Gcetziana of 

 the Cretaceous of Quedlinburg, we find twenty-three species referable to 

 the section of dentate leaves. Of these, none is Cretaceous and none is 

 exclusively North American. Four are Eocene, one Oligocene, seventeen 

 Miocene, and one Pliocene or Quaternary. Salix varians, common in Europe, 

 has been recognized in the Miocene of Alaska and in the upper divisions of 

 the same formation in California. S. Lavateri and S. macrophylla are also in 

 the Miocene of Europe and in that of Alaska. Of the thirty-six fossil 

 species of Willows with entire leaves, eight are Cretaceous, six from the 

 American Dakota group, and two from Europe. No Eocene species is known 

 from Europe, but we have in the American formation one Miocene European 

 Willow, (Sa/i.r Integra, Goepp., discovered in the Eocene strata of Black Buttes, 

 Wyoming Territory, and one species peculiar to this continent,AS'.teZ)tf/am, from 

 the same Eocene formation in the State of Mississippi. 8. angustata, S. elongata, 

 and S. media are European and American Miocene species, while two others, 

 S. Rheana and S. Grmnlandica, belong exclusively as yet to Greenland. An 

 American form, S. Worthenii, is from the chalk bluffs of the Mississippi, a 

 Pliocene formation. It is represented as yet by a single leaf, and may be 

 recognized, when other specimens are obtained, as identical with one of 

 our living species. 



