which are characterised by phenomena of the highest interest. Mr. Webster, in his admirable

geological memoir on the Isle of Wight, first directed attention to these remarkable deposits. Upon

TAB. 69.-SECTION OF A QUARRY IN THE ISLE OF PORTLAND. (From Dr. Fitton's Memoir on the Strata below the Chalk.)

the upper layer of marine limestone (Tab. 69, 8), which abounds in ammonites, trigoniæ, and other characteristic shells of the oolite, is a fresh-water limesto ne, covered by a layer of bituminous earth,

or vegetable mould (4), which (as you may perceive from these specimens, collected a few years since,) is of a dark brown colour, contains a large proportion of earthy lignite, and, like the modern soil on the surface of the island, many water-worn stones. This layer is termed the dirt-bed by the workmen ; and in and upon it are trunks and branches of coniferous trees, and plants allied to the recent cycas and zamia. Many of the trees, as well as the plants, are still erect, as if petrified while growing undisturbed in their native forests, having their roots in the soil, and their trunks extending into the upper limestone (see Tab. 69, 4). As the Portland stone lies beneath these strata, which are not much used for economical purposes, the fossil trees are removed, and thrown by as rubbish. On my visit to the island in the summer of 1832, the surface of a large area of the dirt-bed was cleared, preparatory to its removal, and a most striking phenomenon was presented to my view. The floor of the quarry was literally strewn with fossil wood; and I saw before me a petrified, tropical forest, the trees and the plants, like the inhabitants of the city in Arabian story, being converted into stone, yet still maintaining the places which they occupied when alive! Some of the trunks were surrounded by a conical mound of calcareous matter, which had evidently once been earth, and had accumulated around the bases and roots of the trees. The stems were generally three or four feet high, their summits

being jagged and splintered, as if they had been torn and wrenched off by a hurricane,—an appear. ance which many trees in this neighbourhood, after the late storm, strikingly resembled. Some of the trunks were two feet in diameter; and the united fragments of one tree measured upwards of thirty feet in length; in other specimens, branches were attached to the stem. In the dirt-bed, there were many trunks lying prostrate, and fragments of branches. The fossil plants are called Cycadeoidea by Dr. Buckland, from their analogy to the recent cycas and zamia; but M. Adolphe Brongniart has established a new genus for their reception, which he has named Mantellia. The plants occurred in the intervals between the trees; and the dirt-bed was so little consolidated, that I dug up with a spade, as from a parterre, several specimens that were standing on the very spot in which they grew, having, like the columns of Puzzuoli (Tab. 14), preserved their erect position amidst all the revolutions which had subsequently taken place, and beneath the accumulated spoils of numberless ages. The trees and plants are completely petrified by silex, or flint; you perceive that

These plants are so common in green-houses, that their forms must be well known. In the conservatories of the Coliseum, in the Regent's Park, are fine examples of the dracena, yucca, cycas, and several species of palms, allied to the fossil plants of Tilgate Forest. The magnificent collection of palms of the Messrs. Loddige, of Hackney, is alluded to in my work on the Fossils of Tilgate Forest.

sparks are emitted upon striking a piece of steel with this fragment of what was once a delicate plant; the common forms of the fossil cycadea,

TAB. 70.-SILICIFIED TRUNK OF MANTELLIA NIDIFORMIS.
(Cycadites megalophyllus, Dr. Buckland.*)

"a, Central mass of cellular tissue; b, Circle of radiating woody plates; c, Circle of cellular tissue; d, The case, or false bark.

(Mantellia nidiformis of Brongniart, Tab. 70), are called crows' nests by the quarry-men. Our limits will not admit of a more extended notice of these Dr. Buckland's Bridgewater Essay, Pl. 60.

extraordinary phenomena, and I refer you to the memoirs of Mr. Webster, Dr. Fitton, and Dr. Buckland. From what has been stated, it is evident, that after the marine strata forming the base of the Isle of Portland were deposited at the bottom of a deep sea, and had become consolidated, the bed of that ocean was elevated above the level of the waters, became dry land, and covered with forests. How long this new country existed, cannot be ascertained; but that it flourished for a considerable period is certain, from the number and magnitude of the trees of the petrified forest. In the Isle of Purbeck, traces of the dirt-bed, with the trunks of trees, are seen beneath the fresh-water limestones

1, Purbeck calcareous slate; 2, Dirt-bed, with trunks of trees; 3, Marine limestone of Portland.

of the weald; a proof, that before the deposition of the Purbeck marble could have taken place, the * Dr. Buckland.