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POPULAR SCIENCE REVIEW. 
It appears, therefore, although only upon strong negative 
evidence, no other being possible, that dicotyledons did not 
exist in floras so remote in age as the Grault. There is even no 
direct evidence that they existed during the Chalk, for no dico- 
tyledons are yet known from it or beds ascertained to be contem- 
porary with it. The date of their first appearance is still 
uncertain ; but in Greenland, a leaf of simple form, ascribed 
to a poplar, is seen with what appears to be evidently a true 
Cretaceous flora. Of the many other so-called Cretaceous dico- 
tyledonous floras, whilst some, as that of Aix-la-Chapelle, are, 
if botanical evidence can yet be said to be of any value, 
probably Eocene ; others appear, at most, to be prae-Eocene. 
Between the Eocene and Chalk there is an immense gap, repre- 
sented elsewhere by important formations, and to this period 
the older dicotyledonous floras may, for the present, be safely 
referred. The true Cretaceous floras are still almost completely 
disconnected from those which are post-Cretaceous ; but we 
know so little of the relative ages of the latter, that it is safer, 
at present, in speculations, to leave out of consideration all 
groups of plants which are from beds whose age is not strati- 
graphically determined. It is most important that the exist- 
ence of this intermediate zone should be clearly recognised, 
and the name made use of by Hector, tc Gretaceo-Eocene ,” might 
well be adopted. The term “ Palseocene,” used by Schimper, 
has been applied to lower or even middle Eocene floras, and 
its continuance would therefore involve much confusion. While 
a special designation is a necessity for infra-Eocene deposits, the 
term Oligocene is, upon plant evidence, wholly unnecessary. 
From Eocene to Miocene there is no break whatever, and an 
Oligocene formation has to be created, so far as plants are con- 
cerned, from even distinctly middle Eocene formations. 
