REVIEWS. 
411 
THE CRETACEOUS FLORA OF AMERICA.* 
A MONG the other valuable results of the United States Geological Survey 
of the Territories, under the charge of Dr. F. V. Hayden, is the memoir 
by Professor Lesquereux on the nature and character of the fossil plants 
obtained from the cretaceous Dakota group. This division, lying at the 
base of the cretaceous series, forms a most important link in the physical 
history of the western portion of the continent, containing as it does one of 
the early proofs of the introduction on the earth of a vegetation allied to 
our fruit and forest trees. The formation has a vast geographical extension 
both north and south, from the 39° to the 47° of north latitude, but the 
chief fossils obtained from it have been found in the eastern portions of 
Kansas and Nebraska. The interest connected with this flora, first noticed 
by Dr. Hayden in 1853, and belonging to a lower member of the American 
cretaceous formation, is that it presents a tertiary facies, differing essentially 
from the usual Mesozoic flora of cycads, ferns, and conifers, in containing an 
abundance of dicotyledonous angiosperms; for, of the one hundred and thirty 
recognised species, only twenty do not belong to that division of plants. 
Considered as a whole, says Professor Lesquereux, most of the types of the 
Dakota group related to ; those of our present flora represent a moderate 
climate, like the one prevailing now between the 30° to 45° north latitude. 
The vegetable types more distinctly characterised by their leaves, and which 
are recognised by all the palaeontologists — Salix, Platanus, Sassafras, Aralia , 
Magnolia, Lirisodendron, Menispermum, Rhus, &c. — are all co-ordinate to 
identical climatic circumstances, or to the same average temperature which 
governs at our time the vegetation of the latitude indicated above. All 
these types are, therefore, present in the North American flora, some of them 
with scarcely any alteration of forms. Professor Lesquereux remarks that, 
on account of the deficiency of materials for comparison, there is little to 
say on the relation of the Dakota group flora with that of any of the creta- 
ceous groups of Europe; still there is sufficient to prove with our present 
knowledge the truth of the assertion that the flora of the Dakota group, 
without affinity with any preceding vegetable types, without relation to the 
flora of the lower tertiary of our country, and with scarcely any forms refer- 
able to species known from coeval formations in Europe, presents in its 
whole a remarkable and, as yet, unexplained cause of isolation. Geologists 
must thank Professor Lesquereux for this important contribution to Paleo- 
botany, not only for the detailed description of each species and the careful 
illustration of their forms on thirty well-executed plates, but also in bringing 
before us in a clear and interesting manner the character of the land vegeta- 
tion of the cretaceous period in Western America, so as to contrast or com- 
pare it with the terrestrial floras of the synchronous period in Europe, and 
thus assisting us to restore in part the extent and nature of the land surface 
bordering the old extensive chalk sea, whether in some cases it was low 
islands or low shores, or in others hills and dry lands upon which the trees 
grew. 
* a Contributions to the Fossil Flora of the Western Territories.” Part 
I, a The Cretaceous Flora.” By Leo Lesquereux. Washington: 1874. 
