304 
ELEMENTS OE GEOLOGY, 
now belonging to Australia, and Leucospermum, species of 
which form small bushes at the Cape. 
The epidermis of the leaves of many of these Aix plants, 
especially of the Proteacese, is so perfectly preserved in an 
envelope of fine clay, that under the microscope the stomata, 
or polygonal cellules, can be detected, and their peculiar ar¬ 
rangement is identical with that known to characterize some 
living Proteaceae (Grevillea, for example). Although this 
peculiarity of the structure of stomata is also found in plants 
of widely distant orders, it is, on the whole, but rarely met 
with, and being thus observed to characterize a foliage pre¬ 
viously suspected to be proteaceous, it adds to the proba¬ 
bility that the botanical evidence had been correctly inter¬ 
preted. 
An occasional admixture at Aix-la-Chapelle of Fucoids and 
Zosterites attests, like the shells, the presence of salt-water. 
Of insects. Dr. Debey has obtained about ten species of the 
families Curculionidae and Carabidse. 
The resemblance of the flora of Aix-la-Chapelle to the ter¬ 
tiary and living floras in the proportional number of dicoty¬ 
ledonous angiosperms as compared to the gymnogens, is a 
subject of no small theoretical interest, because we can now 
affirm that these-Aix plants flourished before the rich reptil¬ 
ian fauna of the secondary rocks had ceased to exist. The 
Ichthyosaurus, Pterodactyl, and Mosasaurus were of coeval 
date with the oak, the walnut, and the fig. Speculations 
have often been hazarded respecting a connection between 
the rarity of Exogens in the older rocks and a peculiar state 
of the atmosphere. A denser air, it was suggested, had in 
earlier times been alike adverse to the well-being of the high¬ 
er order of flowering plants, and of the quick-breathing ani¬ 
mals, such as mammalia and birds, while it was favorable to 
a cryptogamic and gymnospermous flora, and to a predomi¬ 
nance of reptile life. But we now learn that there is no in¬ 
compatibility in the co-existence of a vegetation like that of 
the present globe, and some of the most remarkable forms 
of the extinct reptiles of the age of gymnosperms. 
If the passage seem at present to be somewhat sudden 
from the flora of the Lower or ISTeocomian to that of the 
Upper Cretaceous period, the abruptness of the change will 
probably disappear when we are better acquainted with the 
fossil vegetation of the uppermost beds of the Neocomian 
and that of the lowest strata of the Gault or true Cretaceous 
series. 
Hippurite Limestone. —Difference between the Chalk of the 
North and South of Europe. By the aid of the three tests, 
