stone plant, has attracted particular attention, but appears to have foiled every one who has attempted to explain its original nature and mode of existence.

Fig. 61.

Fig. 62.

The subjoined cuts will give a good idea of this strange antediluvian. It is described by Mr. Martin, to have a sub-cylindrical, subramose, tuberculated trunk, fig. 61, with suppressed tubercles set in quincunx order, a, having linear, lanceolated leaves, fig. 62, b, horizontally disposed. In some parts, is a deep, longitudinal sulcus, or furrow, as seen at c, fig. 61; beneath which, is a rough, imbricated body, of a slender, cylindrical form, exposed at d, fig. 62. This, Mr. Martin supposes, after a certain distance, strikes out laterally, and forms a branch: the trunk is then continued for some length, without the furrow, or imbricated body, after which, this again appears, and another branch is thrown out in a different direction.

Various opinions have been entertained respecting this interesting fossil, so unlike any of the vegetables of the present day. Mr. Parkinson had conjectured that it belonged to some body resembling the strobilus, or cone of some vegetable, while Mr. Martin describes it as above. The Rev. Mr. Steinhauer has since studied this fossil, and concludes that the bodies supposed by Mr. Martin to be leaves, were cylindrical fibres, which shot out of the trunk, while the plant grew in a horizontal posture. He supposes that it grew in this direction, in the soft mud at the bottoms of lakes or seas-that it had no branches, but sent out fibres on all sides; and that it was furnished in the centre with a pith, of a structure different from the surrounding wood.

Fig. 63.

But the ingenious author of these observations has omitted to notice the imbricated, or reticulated surface of the central substance, referred to above, and which Mr. Parkinson thinks will afford some information. These configurations, undoubtedly depended on the attachment of some parts of the vegetable, and probably were the bases on which were placed those delicately formed, tubular processes, represented by fig. 63, a, which are seen to pass from the internal substance, to the surface of the body.

From all the information that has been obtained, it is supposed by naturalists, that the Phytolithus verrucosus, was a plant of the succulent tribe, differing from vegetables of the present world, by its containing a more solid part within its succulent substance, from which proceeded a delicate organization by which a communication was preserved with the external surface. It also appears that the species of this genus, distinguished by their characteristic markings, may have been numerous.-Parkinson's Organic Remains, and Trans. Am. Philo. Soc., New Series, vol. i.

Fig. 64.

Phytolithus cancellatus. (Cross barred stone plant.) Mr. Steinhauer has taken much pains to detect and explain the different appearances which this species presents. He has ascertained that there are three distinct kinds of configurations, proceeding from it, originating in the epidermis, the bark, and that which may be considered as holding the situation of the wood of the plant. The first, or epidermal part, is formed of rhombs, divided by lines, forming a network in a manner difficult to express, either by drawings or descriptions, and which leaves the rhombs still approximate.

The impression of this part, is represented by fig. 64. In the second, or the cortical part, the lines between the rhombs are of more breadth, the ridge broader, and less defined and forms with the contracted superior elevation, a protuberance, and the central part assumes the figure of a squamula. Fig. 65, represents the matrix or cast of this part. The third or ligneous, configuration, differs extremely from the two former, and only close observation determines that it originates from the same plant. The cancillated appearance is here entirely lost; the surface is slightly striated with a scarcely perceptible rising under the central ridge, and a minute, but distinctly raised dot Fig. 66.

in the place of the depression

in the epidermis. It has all the appearance of a peeled plant, which has been furnished with small branches, set in quincuncial order. This is represented by fig. 66.

Eight species of this genus are described, but the plan of this work forbids further detail.

In some instances, trees of large dimensions, have been discovered in the fossil state, but these are mostly of the Monocotyledonous kinds, as the palms and tree

like ferns.

In the quarry of sandstone, belonging to the coal formation, on which the city of Glasgow is built, the quarrymen came upon a tree in its place, and just as it had been growing. The trunk is about twenty-six inches in diameter, not quite round, but somewhat oval, so that the north and south diameter is several inches longer than the east and west. The body of the tree is composed of sandstone precisely similar to the rest of the quarry; but the bark has been converted into perfect cherry coal, which adheres firmly to the stone tree, and renders it easy to remove the rock with which it is incrusted. About three feet of the bottom of the tree has been uncovered; this portion is situated about forty feet below the surface, in a

solid quarry of sandstone. The upper part of the trunk and branches have not been uncovered. The roots may be seen dipping down into the earth precisely as the roots of living trees do. Four very large roots may be seen issuing from the trunk, and extending, some of them, about a foot before they are lost in the surrounding stone. There is nothing to indicate the species of tree, of which the mould has been thus preserved. From the appearance of the roots it is obvious, however, that it was not a fir.

This petrifaction demonstrates, that the sandstone has been formed at some period since the growth of large trees, and that the water worn appearance of the quartz pebbles, of which the sandstone is composed, is not a deceitful indication.

Petrifactions. There is a popular opinion that in the process of petrifaction, wood is changed to stone. The truth appears to be, that as the wood decays, its place is supplied by particles of stony matter, deposited from water; and as those particles are exceedingly small, and the decay of the wood slow, its fibrous structure is preserved in the stone, after the wood has entirely disappeared. Wood never undergoes this change when in a state of soundness and integrity; but only when it becomes spongy by decay, and when all its constiuents have disappeared except the woody or ligneous fibre. This is proved by most specimens of petrified wood, which show a partial decay before the process of mineralization began. There are two kinds of petrifactions; the one caused by the infiltration of calcareous, and the other of silicious particles.

Calcareous Vegetable Fossils. Lime is not very frequently the mineralizing matter of vegetable fossils; it is, however, sometimes found introduced into the remains of wood in the form of spar, or imperfect crystals; in the compact form, it is also found filling the interior of fossil reeds and succulent plants.

Silicious Vegetable Fossils. These are immediately distinguished from the calcareous, by their greater hardness, the former giving fire with steel, while the latter are easily scratched with a knife. The silicious fossils are remarkable for the correctness with which the fibres, and markings of the wood have been preserved.

The color is generally greyish, or yellowish white, sometimes passing into brown, and is easily broken into sharp edged fragments. It is found in many parts of the world, but the finest specimens are said to come from Hungary. The English, Portland limestone, contains large fragments of wood, petrified by silicious infiltration, the interstices often containing fine crystals of quartz.

These petrifactions prove that silicious matter is soluble in water, under ordinary circumstances, and that it not only takes the form of the woody fibre, but also of crystals.

Dr. Macculloch has shown also, that in many instances, the mosses and other small vegetables, become encrusted with silicious matter, while in their vegetable state, and are thus preserved from decay. But these real cases, must be distinguished from the black, tree-like appearances which are often seen on the flat surfaces of limestone, and which are produced by oxide of iron, or manganese.

Fig. 67.

The vegetable matter is easily detected by mixing a little of the moss agate, ground fine, with some black oxide of copper,-exposing the mixture to heat, in a glass tube, stopped at one end, and bent so that the other may dip in lime water contained in a vial. If any vegetable matter be present, carbonic acid gas will form, and passing into the lime water, will give it a turbid or milky appearance.

The adjoining cut represents a specimen of moss, apparently belonging to the genus hypnum, contained within a silicious deposite, called chalcedony. In some instances of this kind, the vegetable form is so perfectly preserved, that the plant seems to float as if in a liquid. Even the green color occasionally is preserved, and, in a few instances, the species has been determined.