496 TRUNKS AND SCALES ONLY PRESERVED. 
As no leaves have yet been found with the 
fossil Cycadeas under consideration, we are li- 
mited to the structure of their trunk and scales, 
in our search for their distinguishing characters. 
I have elsewhere (Geol. Trans. London, N. S. 
vol. ii. part iii. 1828) instituted a comparison be- 
tween the internal structure of two species of 
these fossil trunks, and that of the trunks of a 
recent Zamia and recent Cycas.* 
a temporary forest, during an interval which is indicated by the 
thickness of a bed of black mould, called the Dirt bed, and by 
the rings of annual growth in large petrified trunks of prostrate 
trees, whose roots had grown in this mould. 
Thirdly. We find this forest to have been gradually submerged , 
first beneath the waters of a freshwater lake, next of an estuary, 
and afterwards beneath those of a deep sea, in which Cretaceous 
and Tertiary strata were deposited, more than 2000 feet in thick- 
ness. 
Fourthly. The whole of these strata have been elevated by sub- 
terranean violence, into their actual position in the hills of Dor- 
setshire. 
We arrive at similar conclusions, as to the alternate elevation 
and depressions of the surface of the earth, from the erect posi- 
tion of the stems of Calamites, in sandstone of the lower Oolite 
formation on the eastern coast of Yorkshire. (See Murchison. 
Proceedings of Geol. Society of London, p. 391.) 
* M. Ad. Brongniart has referred these two fossil species to a 
new genus, by the name of Mantellia nidiformis and Manteliia 
cylindrica; in my paper, just quoted, I applied to them the pro- 
visional name of Cycadeoidea megalophylla and Cycadeoidea 
microphylla; but Mr. Brown is of opinion, that until sufficient 
reasons are assigned for separating them from the genus Cycas 
or Zamia, the provisional name of Cycadites is more appropriate, 
as expressing the present state of our knowledge upon this sub- 
ject. The name Mantellia is already applied by Parkinson (Tn- 
trodnction to Fossil Org. Rem. p. 53) to a genus of Zoophytes, 
which is figured in Goldfuss, T. vi. p. 14. 
