jet, which is found, especially in the neighbourhood of Whitby, in Yorkshire, in a state very nearly approximating to that of Bovey coal.....Jet is found in other situations, in a different form; resembling, in its shape and the markings of its surface, parts of the branches and trunks of trees, but rarely possessing, internally, any marks of vegetable origin; a circumstance easily accounted for, if its previous softening be admitted.' p. 7.

The evidence for this transition, given by M. M. Chaptal and Fourcroy, though omitted by our Author, is still more decisive. The latter mentions a specimen in which the one end was obviously wood but little changed, and the other pure jet. The former transmitted to the cabinet of Languedoc, several speci mens which were ligneous externally, and perfect jet in the internal parts, distinctly exhibiting the transition of the one into the other. According to Chaptal also, there have been dug up at Montpellier, whole cart-loads of trees converted into jet; their original forms being so distinctly preserved, that he could often detect the species to which they belonged. He instances a walnut-tree completely converted into jet, found at Vachey, and a specimen of a beech similarly changed, from Bosrup in Scania. The same distinguished Author found a wooden pail, and also a wooden shovel, converted into pure jet. It would shew, we think, a very sceptical spirit, to hesitate in our deci sion, after such proofs, resting on the testimony of men so eminent in science.

The next class are those vegetable substances which may be more correctly said to be petrified, than the bituminated sorts. The stony materials which are most usually found to constitute petrifactions of this description, are flint, lime, and bituminous earth, of which the flint is by far the most common. There is often a new transmutation, or change of substance, in the fossil vegetable; but sometimes there is only an earthy impregnation. The stony matter, especially in flint, is commonly diffused through every part of the petrified mass, and seems to be ultimately united with their integral molecules. It has been principally formed in minute crystallizations, which, by mutual and regular apposition, have gradually formed a concrete substance; a process plainly indicated by most of the specimens of this kind having an investiture or crust of extremely minute crystals, which are sometimes even visible on each fascicle of the fibres, and on the sides of interstices and cavities. Of wood so petrified, there seem to be two sorts, namely, that which has, and that which has not, undergone bituminous fermentation. The latter is usually in the state of rotten wood as to its texture, but its specific gravity soon undeceives those who suppose it to be wood of this kind.

That sort of petrified wood which partakes of the nature of Chalcedony, Jasper, Opal, or Pitchstone, has commonly a conchoidal fracture, a dark bituminous colour within, although whitish externally, and gives sparks when struck with steel. The fibres are penetrated with the flinty matter, but no bituminous substance is found intermixed with the flint, or having a tendency to colour it; and when the silex has got to the surface, or into a cavity, it often assumes a mammillated form, and becomes transparent. It is often bestudded with fine, small quartz crystals: some specimens seem to have been attacked by the teredo, and have the small holes filled with transparent flinty matter. Another sort is marked with coloured delineations, like the compound pebbles called agates; this kind is usually more transparent than the former, and has a more vitreous lustre. Mr. Parkinson is of opinion, that all jasperine minerals, if they do not originate from vegetable materials, are closely connected with them. In some of them, we have distinctly seen the rings marking the annual growth of the original tree, and even the delicate wavings of the fibrilla around what seems to have been a knot, or the off-going of a branch.

A not less interesting species of petrified vegetable productions than the flinty, is the calcareous. The formation of the latter, however, it is not so difficult to understand and explain. It is often carried on almost under the eye of the observer, in the case of the numerous calcareous springs, which, by depositing their lime, form incrustations on every thing they meet in their course. This process takes place to a great extent, at Matlock in Derbyshire, and at Tivoli in the vicinity of Rome: the waters at the latter place deposit lime and stone tuba so copiously, as to afford abundant materials for architectural purposes. It consequently happens, that whatever substances come in the way of these copious precipitates, are enclosed in the mass, and, if their texture will admit, are penetrated with it in all directions. The inhabitants of Matlock, as is well known, take advantage of this, to procure curious petrifactions of birds-nests with their eggs, wigs, besoms, and other things calculated to excite wonder by their conversion into stone by calcareous incrustation. In Italy and Peru, it has been turned to account in the making of busts, casts, and impressions of medals. It is worthy of remark, that, while the lower part of a stem of moss has been thus incrustated, the upper part sometimes has continued to vegetate, in the same way as mosses grow in peat bogs after their roots have perished. Botanists account for this from the singular nature of mosses, which grow

from points in a great degree insulated with respect to the

root.

The mineralization of vegetable substances by the metals, is a circumstance of frequent occurrence, and seems to take place much in the same way as the petrifactions already mentioned; namely, by the vegetable substance being penetrated with the metallic, either in a mechanical or a chemical manner. The first of these which merit our attention, have been called pyrites, from their often taking fire spontaneously when they come into contact with moisture. The woods which are properly denominated pyritical, have commonly a splendid metallic appearance, and are of a high specific gravity, while traces of their original texture are sometimes very obvious. Even the annual rings of the wood are occasionally found beautifully bestudded with the pyrites, whose surfaces often shew a fine play of iridescent colours.

In some specimens, in which the general appearance is that of bituminous wood, the metallic impregnation can only be detected by the weight of the fossil, and the blue or green hue on its surface. Cupreous wood in this state forms very beautiful specimens, displaying, not only on its surface, but in its substance, mingled with the charred wood, the most vivid blue and green colours, with patches of the carbonate in the state of malachite. The finest specimens of cupreous wood are obtained from the copper mines of Siberia.' p. 29.

In some specimens of a similar sort, the species of the tree so changed is often easily recognised. The birch and beech have been mentioned, of which the first often preserves its delicate white cuticle with its original texture. In some cases, the structure of rotten wood is very distinct, and also the different parts of the trees, as the stem, branches, twigs, leaves, and roots. The grassy turf of the soil also, with all the vegetable exuvia which may be scattered upon it, are, on exposure to mineral springs, commonly rendered metallic. In Mexico, wood tin occurs, along with mammillated chalcedony. When it is recollected, that even in our herbaria, when every attention has been paid to the preservation of specimens, the ascertaining of distinctive characters is often a matter of considerable difficulty, it may be easily imagined, that it will be a still harder task in those which have been converted into stony and metallic substances. Yet, the distinctive characters of species are often to be recognised in fossil vegetables; and mineralized wood has been found, which proved to be beech, ash, willow, walnut, hazel, birch, pine, and many other kinds. The conjectures of fancy have been very fertile in discovering

petrified remains of wood fashioned by the hand of man. It has been asserted, for instance, that the pieces of wood got from the Thames, are stakes which were driven into its bed by the Romans; when the fact is, that a stratum of piles quite similar is found to extend over a considerable part of the adjacent fields. Some classes and genera of vegetables appear to be more easily converted into stone than others. Thus we are told by Mr. Wallis in his History of Northumberland, that the mosses and liverworts of a petrifying brook become stony, while the primroses and geraniums are quite untouched, and receive from it no foreign investiture or incrustation.

It is a curious fact with regard to the vegetable remains, or rather the impressions of vegetables, which are found in schistus, that when the lamina, or the nodules containing them, have been split, the two plates of the stone display the same side of the leaf.

The explanation of this curious circumstance, which long puzzled the oryctologists, is found in the vegetable matter, during its passing through the bituminous change, having become softened, and having filled its own mould with its melted and softened substance; the nodule, on being broken, shewing on one side the surface of the adherent bituminous cast, and, on the other, the correspondent mould.' p. 10.

The zoophytes are the first species of living beings which are met with in rocks, when arranged according to their supposed relative antiquity. It is said, that, in the primitive rocks of Werner, no such remains exist, but that they begin to appear in transition rocks. However this may be, they

are found in the newest depositions, even in alluvial soil: for example, in the Isle of Bute, considerably above the sea-mark, Professor Jameson found a small bed consisting chiefly of the millepora polymorpha. Among the least perfect of the zoophytes, Mr. Parkinson places the genus sponge, concerning the nature of which many conjectures have been offered. In a note, he introduces the following interesting notice of this subject.

Sir Humphrey Davy had procured iodine from several of the fuci and ulvæ, but not from the alkaline matter manufactured at Sicily, Spain, and the Roman States; nor did he find that the ashes of coral or of sponge appeared to contain it. From various experiments, Dr. Fyfe was enabled to conclude, that iodine was confined not only to the class cryptogamia, but to the marine productions of this class. Sponge being, however, considered to belong to the animal world, forms an apparent objection to this conclusion. But it must be remembered, that Linnæus was inclined to regard sponge as a vegetable substance, and to place it in the class cryptogamia, subdivision

alga aquatica; but was doubtful of the correctness of this arrangement. "May not the fact," Dr. Fyfe observes, "that sponge contains iodine, be an argument in favour of the opinion of Linnæus, that this substance properly belongs to the vegetable world, class cryptogamia, from the plants of which iodine is obtained?"

note.

A still more recent investigation, however, has discovered iodine in medusa and the polypi known by the name of animal flowers; which is, we think, quite conclusive, so far as this argument goes, that sponge is not a vegetable, but an animal substance.

A singular circumstance was observed by Mr. Parkinson in a tubiporite limestone which he procured from Mendip; namely, the tubes were filled with flint, which took a polish. Does this give countenance to the conversion of animal remains of a calcareous kind into flint, as maintained by Linnæus and others? We believe that, in the present state of our knowledge, it is wholly inexplicable. Fossil tubipora indeed, like other organic remains, are seldom, perhaps never found in a recent state; and some of them are very unlike any thing which our seas now exhibit. Of this we have a fine example in the catenulata or chain-coral, the small tubes of which, when a horizontal section of them is made, appear in beautiful waved lines formed by the extremities of the tubes like the links of a chain: these wavings frequently approaching or coming into contact with one another, and then receding again, resemble very much the connected mesh-work of a net, or a retiform plexus of lymphatic vessels. In other tubiporites, there is a curious communication of the pipes by smaller tubes radiating from the larger ones, and passing through their contiguous plates of junction.

Some of the madreporites are flattened so as to indicate that they had suffered external compression; but the hardness of their recent encasement previous to any thing like petrifaction, precludes that supposition. A few rare specimens are composed of transparent sparry limestone, and some have figures which the imagination easily construes into the horns. of goats and other animals, the remains of fungi and plants of that sort. These circumstances render a scientific arrangement of them a work of great difficulty, as the labours of their minute architects seem at times to have been modelled by whim and caprice, more than by any instinctive or circumstantial plan of operations. We cannot, however, judge accurately of this, on account of our deficient knowledge of the circumstances which might expedite or retard their work, and make them change their vertical direction to a sloping or