Pl. 57, Fig. 3, exhibits similar stumps of trees rooted in their native mould, in the Cliff immediately east of Lulworth Cove. Here the strata have been elevated nearly to an angle of 45°, and the stumps still retain the unnatural inclination into which they have been thrown by this elevation.
The facts represented in these last three figures are fully described and explained in the paper above referred to; they prove that plants belonging to a family that is now confined to the warmer regions of the earth, were at a former period, natives of the southern coast of England.[1]
As no leaves have yet been found with the fossil Cycadeæ
under consideration, we are limited to the structure of their
dulations, marked in the stone, which surrounds a single stump, rooted in the dirt-bed in the Isle of Portland. This very curious disposition has apparently resulted from undulations, produced by winds, blowing at different times in different directions on the surface of the shallow fresh water, from the sediments of which the matter of this stratum was supplied, while the top of this stem stood above the surface of the water. See Geol. Trans. Lond. N. S. vol. iv. p. 17.
- ↑ The structure of this district affords also a good example of the proofs which Geology discloses, of alternate elevations and submersions of the strata, sometimes gradually, and sometimes violently, during the formation of the crust of our planet.
First. We have evidence of the rise of the Portland stone, till it reached the surface of the sea wherein it was formed.
Secondly. This surface became for a time, dry land, covered by 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 thickness. Fourthly. The whole of these strata have been elevated by subterranean violence, into their actual position in the hills of Dorsetshire. We arrive at similar conclusions, as to the alternate elevation and depressions of the surface of the earth, from the erect position 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, page 391.)
