THE CRETACEOUS FLORA. 
47 
1, the reigTL of Acrogens, characterised by the abundance of 
E quisetacece (horsetails), Lycojpodiacece (clubmosses), Filices 
(ferns) ; 2, the reign of Grymnogens, characterised by the cycads 
and conifers ; 3, the reign of Angiosperms, characterised by the 
exogens and endogens. Not that they are special or peculiar 
to each period, but are the most abundant forms ; so that, instead 
of being a truly consecutive series, they form a more or less 
parallel one ; for in the first period the abundant acrogens are 
associated with some gymnogens in the form of the coniferse, in 
the second period the numerous gymnogens are associated with 
some angiosperms, which latter increase and constitute the domi- 
nant flora of the third period, as shown in the following dia- 
gram : — 
Palaeozoic. Mesozoic. Ccenozoic. 
Exogens. 
Endogens. 
i, Gymnogens. 
Acrogens. 
The earliest well-marked flora is that of the Devonian period, 
as seen in New Brunswick, Ireland, and some other parts of 
Europe. In the underlying Silurian (although traces of Ly co- 
pocls are stated to occur) and in still older strata, the structural 
evidence of plants is very scanty; still the occurrence of anthra- 
cite, veins of graphite, and beds of iron ore, indicate probably 
the existence of a former vegetation, whose original characters 
are so obliterated as to prevent us from determining their real 
affinity.* 
The Mesozoic rocks, characterised by their gymnospermous 
flora, are divided in ascending order into Triassic, Jurassic, 
Purbeck-Wealden, and Cretaceous strata, and it may be interest- 
ing to inquire what was the nature of the plant-life at the close 
of the mesozoic period, and to what extent it was related to a 
preceding, or foreshadowed that of a subsequent period. Com- 
paratively recent discoveries in Europe and America have 
considerably enlarged our knowledge of this old cretaceous 
vegetation, from which it appears that, with some forms in 
common, it is markedly distinct from the lower mesozoic flora, 
and presents the facies of a tertiary flora, especially in the 
abundance of dicotyledonous plants, so much so that in some 
districts the beds containing them were at first considered to be 
of miocene instead of cretaceous age. 
Essentially a marine formation, and consisting of sediments 
* Sterry Hunt, “ Amer. Jour, of Science,” 2nd ser. vol. xxxi. p. 395. 
C. H. Hitchcock, u Geology of New Hampshire,” pp. 508, 509, 
