NOTE II. p. 37.

"Within the last ten years, three large trees have been found in Craigleith quarry, near Edinburgh, which have excited great attention, and have been minutely investigated. In 1826, a tree was exposed, measuring thirtysix feet in length, and three feet diameter at the base; and, in November 1830, one still more remarkable was displayed to view. This tree was found about the centre of the quarry, at a depth from the surface of about one hundred feet. A considerable portion of the top was broken off and destroyed when first discovered; but more care having been observed afterwards, the whole was exposed in such a manner, that its form and size and position, could be well ascertained.

The entire length of this tree was forty-seven feet, exclusive of the top, which was broken off, and supposed to be about twelve feet. Its breadth varied from two to one and a half feet. Its greatest diameter, near the base,

was, in one direction, five feet. It was of a compact solid structure, its original shape apparently well preserved, with the exception of part being somewhat flattened, probably by the unequal pressure caused by one portion becoming consolidated before another, and thus the softer parts giving way. The external surface was incrusted with coaly matter, varying from a quarter to half an inch in thickness, which was evidently the outer portions and bark converted into bitumen. The tree lay in a slanting direction, with its lower end dipping to the south-east. It lay across several strata of sandstone and shale, the upper beds of which rested in an unconformable position on the lower-the latter forming a sort of hollow trough. There were no traces of either branches, leaves, or roots, attached to this fossil; both its upper and lower ends were evidently rounded, and worn smooth by attrition. About a third from the top, it was bent and somewhat flattened; distinct elevations were seen at intervals on the trunk, corresponding to the places where branches may be supposed to have grown.

A branch was discovered a little to the south of the position of this tree in the same year; and, in 1833, another large trunk was exposed in a deeper part of the quarry, about fifty yards to the westward.

This tree lies at an angle of forty-five degrees, and rests on strata, dipping to the east by north. Upwards of thirty feet have been already exposed; the greatest diameter is about three feet; irregular swellings or rings are distinctly visible on the trunk, and two distinct hollows where branches have grown out."-Geology of the Environs of Edinburgh, p. 52.

When the first fossil tree was discovered in Craigleith quarry, near Edinburgh, various conjectures were formed regarding the class of plants to which it be. longed. According to the canons of Brongniart, then in full force, its position in the lower fossiliferous beds ranked it among the arborescent ferns: then, when its structure clearly indicated that it was a tree, a new specific name was given to it, and it was henceforth pronounced an extinct fossil. It might, in this way, according to the prevailing theories, have been for ever, to use an expression of Swift, "kicked out of creation," had not Mr Nicol, after much labour and patient induction, and aided by the lucky chance of receiving a spar of New Holland pine which had been brought to Leith spliced to the mast of a vessel, detected its exact conformity with a recent species. Thus this splendid fossil, instead of obtaining a niche in the archives of a preexisting world, was found to be identical with a species of araucaria, at present flourishing in the islands of the South Sea.

NOTE III. p. 39.

THEORIES OF IGNEOUS ROCKS.

All those speculations regarding the primary condition of matter, and the original formation of the sphere of the earth, are of a very unprofitable nature, in so far as the phenomena attending them cannot be compared to any operations at present in action. It is evident that we now see matter only as it has undergone various chemical combinations and changes, and under forms and obeying laws totally different from its original condition. The oblate spheroidal figure of the earth has been thought to imply a state of fluidity of the whole mass: yet there are no valid grounds for assuming this; for the matter of the globe may just as readily be supposed to have been formed into this particular figure, to suit subsequent laws of rotatory motion, before even the law of fluidity was imposed upon it. Neither are we at all certain whether the globe be a solid sphere of matter with a density increasing towards the centre, or a hollow ball. The experiments of Maskelyne and Playfair, if accurate, would rather indicate the former condition, proving its mean density to be five times that of water. On the other hand, the existence of a highly elastic medium occupying the centre, is not an improbable supposition, and perhaps more in accordance with the economic analogies of nature; for in none other of her works do we witness that prodigal waste (if the term may be allowed) which such an enormous mass of matter, apparently for no immediate use, would indicate. The well known luminous theory of the late Sir John Leslie may thus turn out, after all, a most brilliant idea.

The existence of the different earths which compose the principal mass of the crust of the globe in a metallic state, as shewn by the splendid discoveries of Davy, and

the farther application of these to the origin of volcanic phenomena, as prosecuted by that distinguished philosopher, and by Dr Daubeny, are theories now very generally adopted by geologists. These theories certainly account for the production of all the varieties of igneous rocks in a much more satisfactory way than any other; yet we must by no means conclude, that the discovery of the metallic basis of the earths has brought us to the ultimate elements of things. We know so little of matter, that it may be perfectly possible that it consists of only one simple element, or, to take the Platonie doctrine, two, and that all its varied aspects may be due to the various laws imposed upon it.

If we view the elevation of igneous rocks, then, as portions protruded from the matter of the earth's crust by chemical actions, the magnitude of these, compared to the mass of the earth's diameter, dwindles into mere insignificance, and need not demand any lengthened eras for their production. See Section, Plate IV.

NOTE IV. p. 42.

SUCCESSIVE CREATIONS OF ANIMALS.

"When I endeavour to prove that the rocky strata contain the skeletons of several genera, and the loose strata those of several species, all of which have ceased to be existing animals, I do not pretend that a new creation was required for calling our present races of animals into existence. I only urge that they did not anciently occupy the same places, and that they must have come from some other part of the globe."*

It is somewhat extraordinary that those theorists who profess to draw their deductions exclusively from causes now in operation, should yet so unceremoniously

* Cuvier, Recherches sur les Ossmens Fossiles, tom. i. 1821.