828 The American Geoloyist. November, 1893 
as is yet known the first appearance of angiospertns. The older portion 
of the lower Potomac contains, with a great predominance of Jurassic 
types, a number of old forms of angiosperms, such as Ficophyllum, Pro- 
icaphyllum, Roger6ia, etc. In the upper beds of the same angiosperms 
become more abundant, and they are more modern in type, while the 
Jurassic element is much diminished. The plants found at Glen Rose 
show, so far as can be judged from so imperfect a collection, that the 
Trinity flora finds its closest resemblance in the older portion of the 
lower Potomac. There is, however, this important difference: No trace 
of angiosperm, even the most archaic, has been found in the Texas re- 
gion. We have only the four elements of the typical Jurassic flora. 
This then makes the Trinity flora somewhat older than the oldest Po- 
tomac. The absence of the angiosperms and the presence of the forms 
that are found indicate decidedly that the Trinity flora is not younger 
than the earliest stage of the Cretaceous. The number of plants found 
to be identical with certain of those of the oldest Potomac shows that 
there is little difference in the age of the two formations. The plant - 
bearing portion of the Trinity is somewhat older than the basal Po- 
tomac strata, but the difference in age cannot be great."' 
According to the determinations of Prof. Hill the molluscan marine 
fauna associated with these plants is Neocomian or basal Cretaceous. 
The Flora of the Dakota Group. A Posthumous Work, by Leo Les- 
quereux. Edited by F. H. Knowlton. Monographs of the U. S. Geol. 
Survey, vol. xvii, pp. 400, with 66 plates. Price .$1.10. Washington, 1891. 
This monograph, which was received a few months ago, prejents in 
systematic order a full list of all the plant species thus far discovered 
from the Dakota sandstone formation, chiefly in Kansas, Nebraska and 
Minnesota. Many of the species had been before described by Lesque- 
reux in 1874 and 1883, in bis volumes vi and vm of the final reports of 
the U. S. Geol. Survey of the Territories, under the direction of Dr. 
Hayden. A part of these are here simply noted in the catalogue, with 
references to the places of their original description; but subsequent 
discoveries of better specimens of a large number of these plants, and 
the accession of many new species, led to the present work. Even after 
this work was once completed and forwarded early in 1888 for publica- 
tion, it was recalled to include the exceptionally rich collections of the 
Dakota flora obtained during that year by Mr. Charles H. Sternberg, 
Judge E. P. West, and others in Ellsworth county, Kansas. These lat- 
est additions gave 110 new species, with which the entire known flora of 
this formation is brought up to 160 species. Its European correlative, 
the Cenomanian formation of Middle Cretaceous age, has supplied only 
about 110 plant species; but the Cenomanian schists of Atane, Green- 
land, whose flora has been so thoroughly studied by Heer, contain 271 
species. The nearest relationship of the Dakota flora is with that of the 
Atane beds, the two having 39 species in common, while the whole num- 
ber of Dakota plants known elsewhere, including these of Atane, is 66. 
Perhaps the next most close affinity is shown by the Senonian or Up- 
