302 
ELEMENTS OF GEOLOGY. 
Kent and Surrey, no formation intervenes between these 
beds and the Trias; all intermediate groups, such as the 
Lower Keocomian and Oolite, having either not been depos¬ 
ited or destroyed by denudation. 
Flora of the Upper Cretaceous Period.— As the Tipper Cre¬ 
taceous rocks of Europe are, for the most part, of purely ma¬ 
rine origin, and formed in deep water usually far from the 
nearest shore, land-plants of this period, as we might natu¬ 
rally have anticipated, are very rarely met with. In the 
neighborhood of Aix-la-Chapelle, however, an important ex¬ 
ception occurs, for there certain white sands and laminated 
clays, 400 feet in thickness, contain the remains of terrestrial 
plants in a beautiful state of preservation. These beds are 
the equivalents of the white chalk and chalk marl of Eng¬ 
land, or Senonien of D’Orbigny, although the white siliceous 
sands of the lower beds, and the green grains in the upper 
part of the formation, cause it to differ in mineral character 
from our white chalk. 
Beds of line clay, with fossil plants, and with seams of lig¬ 
nite, and even perfect coal, are intercalated. Floating wood, 
containing perforating shells, such as Pholas and Gastrochoe- 
na, occur. There are likewise a few beds of a yellowdsh- 
brown limestone, with marine shells, which enable us to prove 
that the lowest and highest plant-beds belong to one group. 
Among these shells are Pecten quadricostatus^ and several 
others which are common to the upper and lower part of the 
series, and Trigonia limhata^ D’Orbigny, a shell of the white 
chalk. On the whole, the organic remains and the geologi¬ 
cal position of the strata prove distinctly that in the neigh¬ 
borhood of Aix-la-Chapelle a gulf of the ancient Cretaceous 
sea was bounded by land composed of Devonian rocks. 
These rocks consisted of quartzose and schistose beds, the 
first of which supplied white sand and the other argillaceous 
mud to a river which entered the sea at this point, carrying 
down in its turbid waters much drift-w^ood and the leaves 
of plants. Occasionally, when the force of the river abated, 
marine shells of the genera Trigonia^ Tiirritella^ Pecten^ etc., 
established themselves in the same area, and plants allied to 
Zoster a and Fueus grew on the bottom. 
The fossil plants of this member of the upper chalk at Aix 
have been diligently collected and studied by Dr. Debey, 
and as they afford the only example yet knowm of a terres¬ 
trial flora older than the Eocene, in which the great divis¬ 
ions of the vegetable kingdom are represented in nearly the 
same proportions as in our own times, they deserve particu¬ 
lar attention. Dr. Debey estimates the number of species 
