DICOTYLEDONS OF THE CRETACEOUS EPOCH. 205 
and pebbles ; another elevatory movement must have raised 
_the entire series of deposits to their present situation, and 
_the retiring waters have removed the loose portions of the 
last formed strata, and dispersed them, with fragments of the 
Silicified trees, over the surface of the Egyptian and Lybian 
- deserts.* 
DicoTYLEDONS OF THE CrEeTAcEous Epocu.—Among the 
_ crowd of interesting facts relating to the botanical character 
_ of the earlier periods of geology which recent observations 
_ have brought to light, one discovery demands especial notice, 
and I have reserved it for this place, rather than introduce 
_ it in an earlier section. 
In the neighbourhood of Aix-la-Chapelle the lower mem- 
4 bers of the Cretaceous formation, viz. the Greensand, Galt, 
and Chalk-marl, are well developed, and comprise a series 
of littoral deposits of the great Chalk ocean that extended 
_ westwardly between een. and England, on both sides of 
- the existing Channel, and ee over North and Cen- 
‘ tral Germany, Sweden, Poland, and Kussia, far into Asia. 
The series of strata at Aix-la-Chapelle is several hundred 
_ feet in thickness, and the lowermost beds lie immediately 
_ on the Carboniferous rocks of the country. 
Dr. M. H. Debey,t to whose scientific labours we are in- 
_ debted for an accurate knowledge of these interesting facts, 
_ divides these cretaceous depen into four groups, the lower- 
most of which appears to be the equivalent of our Green- 
sand ; it consists of beds of clay and sand, the middle portion 
ke abounding in stems, leaves, and fruit, and the resin of coni- 
_ ferous trees. 
The epidermis of the leaves often occurs in a carbonized 
state, and is recognizable by its microscopic structure. 
_ * See a Memoir on the Geology of Egypt, Geol. Proc. vol. iii. p. 782 ; 
and on the Petrified Forest near Cairo, vol. iv. p. 349, by Lieut. New- 
bold, F.R.S. 
+ See Geol. Journal, vol. vii. p. 109. 
