40 FOSSIL FLORA OF THE SIERRA NEVADA. 
was a mere beginning of a scientific exposition of general interest. For 
the presence of highly developed vegetable types in the Cretaceous was 
a fact as surprising to European paleontologists as to those of this con- 
tinent, and of course induced more extensive and careful researches in 
the same field. 
In 1866 Heer published the Phyllites Crétacées du Nebraska, from speci- 
mens collected by Professors Marcou and Capellini in a tour of explora- 
tion especially undertaken for the purpose of ascertaining the «accuracy 
of the geological determination of the deposits where the so-called Cre- 
taceous leaves had been found. Seventeen species or vegetable forms 
are described and figured in this memoir. Later, in 1868, two other 
papers were prepared from specimens of Cretaceous leaves collected by 
Professor F. V. Hayden, — one by Professor Newberry, the other by myself. 
Both are without figures, intended merely as an exposition of specific 
characters of plants which had to be more fully described in monographs. 
The plates of eighteen species prepared by Professor Newberry for his 
work have been engraved, but not yet published. 
The number of specimens of Cretaceous plants having been consider- 
ably increased by the explorations of Professor Hayden and myself in 
Nebraska and Kansas, I was requested to prepare for publication all the 
vegetable Cretaceous forms which were then under examination; and 
these were described and figured in the sixth volume of the Report of 
the United States Geological Survey of the Territories, 1874. This work 
represents one hundred and thirty Cretaceous species, figured in thirty 
plates. In the following year I made a revision of this volume in the 
Annual Report of Dr. F. V. Hayden, with description and figures of 
twenty-six new species, from specimens received after the publication of 
the Cretaceous flora. Thus, from the different works mentioned above, 
the Cretaceous flora of this continent is represented by about two hun- 
dred specified forms. 
Our acquaintance with the vegetable paleontology of the North Ameri- 
can Tertiary has been also widely advanced of late, especially by the 
United States geological explorations of the Western Territories under 
the direction of Dr. F. V. Hayden. In 1860 this Tertiary flora was repre- 
sented merely by six species, described and figured by Professor J. D. 
Dana in the Report of the United States Exploring Expedition under 
the command of Lieutenant Charles Wilkes, from materials found on the 
