seven years three bignonias in the plantations surrounding his house had been struck by lightning, although these shrubs were topped on all sides by larches, pines, acacias, and plane trees.

In the "Gardener's Chronicle," a few months ago, it was stated that a common oak-tree in Scotland had been struck by lightning some years before; and on recovering from its injury, it was remarked in the following spring that the leaves were variegated, and it is said that they have continued to be so every year since. A verification of this statement would be desirable.

On the Aqueous Origin of Granite. By ALEXANDER BRYSON, F.R.S.E.*

For many years after Dr William Smith, the father of English geology, had published his "Tabular View of the British Strata," in 1790, geology was studied only in the direction of paleontology. Physical, chemical, and dynamical geology were left by the great masters of the science almost unregarded since the early years of the Royal Society of Edinburgh, when its meetings were made brilliant by discussions on the theory of the earth, the formation of granite, trap, and porphyry, by Hutton, Hall, and others. When Dr Smith announced his great discovery, that fossils prove the relative ages of formations, geologists were naturally tempted to leave their former fields of inquiry as barren, and enter with enthusiasm on the study of paleontology, as promising richer results; thus, for nearly half a century they were content to receive the speculations of Hutton and the experiments of Hall as demonstrative of the plutonic origin of the primary rocks.

In attempting to prove the aqueous origin of granite, I will not adduce any views trenching on the domain of the theologians who assailed Hutton and his followers, believing as I do that geology has no necessary connection with cosmogony -metamorphosis, not morphism, being its proper study.

* Read before the Royal Society of Edinburgh, April 29, 1861.

Speculations on the origin of granite are nearly coeval with the foundation of this Society. In the first volume of its Transactions, Hutton has stated, in his celebrated paper on the Theory of the Earth, "That the nature of granite, as a part of the structure of the earth, is too intricate a subject to be here considered, where we only seek to prove the fusion of a substance from the evident marks which are to be observed in a body." "We shall therefore only now consider one particular species of granite; and if this shall appear to have been in a fluid state of fusion, we may be allowed to extend this property to all the kind. The species now to be examined comes from the north country, about four or five miles west from Portsoy, on the road to Huntly. I have not been upon the spot, but am informed that this rock is immediately connected or continous with the common granite of the country. This, indeed, appears in the specimens which I have got, for in some of these there is to be perceived a gradation from the regular to the irregular sort. This rock may indeed be considered, in some respects, as a porphyry; for it has an evident ground, which is felspar in its sparry state; and it is in one view distinctly maculated with quartz, which is transparent, but somewhat dark coloured. Considered as a porphyry, this specimen is no less singular than as a granite. For instead of a siliceous ground maculated with rhombic felspar, which is the common state of porphyry, the ground is uniformly crystallised, or a homogenous regular felspar maculated with the transparent siliceous substance. But as, besides the felspar and quartz, which are the constituent parts of the stone, there is also mica, in some places it may with propriety be termed a granite." Hutton further states, "that it is evident from the inspection of this fossil that the sparry and siliceous substances had been mixed together in a fluid state, and that the crystallisation of the sparry substance, which is rhombic, had determined the regular structure of the quartz, at least in some directions."

The mineral here alluded to by Hutton is the well-known graphic granite of Portsoy. Where he found the evidences of its fluid fusion I have not been able to discover; that it was in aqueous solution, I shall attempt in the sequel to show. This

was a very narrow basis on which Hutton reared so large a generalisation that the granites were of igneous origin, but Sir James Hall came to his aid, and most ingeniously endea voured to strengthen Hutton's position. On this point Sir James Hall remarks, "To a theory, however, which embraces so great a variety of objects, some difficulties must be expected to occur, and this. is the more likely to happen that, though the agents employed in it be such as we are well acquainted with, yet they are introduced as acting in circumstances very different from those in which we usually see them act. Of these difficulties the most considerable appeared to him to be the following: In granite, which contains quartz and felspar, it frequently occurs that felspar is seen with the form of its crystals distinctly defined, whilst the quartz is a confused and irregular mass, being almost universally moulded upon the crystals of felspar. Now, were it true that all granite is formed by fusion, the very contrary, it would seem, ought always to take place, as felspar is very easily melted, and quartz resists the greatest efforts of heat that have hitherto been applied to it. This difficulty is obviated thus. It is well known that when quartz and felspar are pounded and mixed together, the mixture may without difficulty be melted and run into a kind of glass, the felspar serving as a flux to the quartz. The same fact may be stated in another way, by considering the felspar when melted as a fluid in which, as in a menstruum, the quartz is dissolved; and in this view we may expect, by analogy, that phenomena similar to those of the solution of salt in water should take place.

"Now it is certain that when excessive cold is applied to salt water, the water is frozen to the exclusion of the salt, the ice obtained yielding fresh water when melted, and the salt, when the experiment is pushed to the utmost, separating from it in the form of sand. Why should not the same thing happen in the solution of quartz in liquid felspar, when the mass is allowed to cool below the point of congelation of the menstruum?

"The felspar may crystallise separately from the quartz, as we have seen pure ice formed separately from the salt, in

both cases the congelation of the solvent being simultaneous to that of the dissolved substance. Hence the crystals may mutually interfere with each other's forms, and we may naturally expect to see quartz moulded on crystals of felspar, or the reverse.

"In answer to an objection which might be urged against this reasoning, viz., that the result of the fusion of granite is a glass in which no crystallisation can be seen, an accidental experiment was produced, which happened at one of the Leith glass-houses a few weeks previous to the reading of this paper. A quantity of common green glass having been allowed in a great mass to cool gradually and very slowly, it was found to have lost all the properties of glass, being opaque, white, very hard and refractory, and wholly composed of a set of crystals which shot into some cavities in a determinal form.

"The same principle seems to point out the theory of all kinds of granite, and shows their connection with one another and with all the other unstratified bodies. If quartz, felspar, schorl, mica, garnet, &c., happen to be melted together, the most fusible substance of them all may be considered as the menstruum in which all the rest are dissolved, and we may suppose that these various dissolved substances may differ amongst themselves in their properties of solution, as salts differ from one another, so that some of them may be more soluble in the menstruum when very much heated than when it is comparatively cold, and others may be as soluble in it when little warmer than its point of congelation as when raised to a much higher temperature." Hall submitted powdered limestone and calc spar to heat and pressure; at fifty atmospheres he obtained a compact limestone, and at eighty-six a crystalline marble. These experiments and generalisations date from the beginning of this century. We can scarcely now appreciate their full intrinsic worth; but how our fathers estimated them is evident, that this experiment of Hall was made the ground of a flag of truce to convey the news of it to the French Academy-a fine instance of the cosmopolitan nature of science.

To these views of Hutton and Hall, Dr Murray, in his "Comparative View of the Huttonian and Neptunian Sys

tems of Geology," thus replies: "The structure and appearances of granite as a fossil have been brought forward by Dr. Hutton as favourable to his hypothesis. There can be no doubt that this rock has at one time been fluid. Its constituent parts, particularly the felspar, and sometimes the quartz, are crystallised, and it not unfrequently contains other crystallised fossils. This fluidity, from which it has been consolidated, Dr Hutton conceives is proved to have been that of fusion, from the parts of the granite impressing each other. The species of granite termed graphic is stated particularly as establishing this deduction. In it the felspar is crystallised in its usual rhomboidal form, and these crystals impress the quartz, put it aside as it were, and give it its particular situation along the side of the rhomboidal felspar " "Hence," says Hutton, "this granite is not a congeries of parts, which, after being separately formed, were somehow brought together and agglutinated; but it is certain that the quartz at least was fluid when it was moulded on the felspar.” And "this fluidity was not the effect of solution in a menstruum, for in that case one kind of crystal ought not to impress another, but each of them should have its own peculiar shape.

Murray further replies, "It has already been shown how simultaneous consolidation may take place from solution, and the structure of granite can from this circumstance furnish no argument against its aqueous origin. But it affords the clearest demonstration that it has not been formed by fusion. Felspar is a substance incomparably more fusible than quartz, the first varying from 120 to 150, the other being 4043 of Wedgewood's scale.

"It is a proposition, therefore, self-evident and undeniable, that in the same mass quartz could not be fluid when felspar was solid; and therefore, since in this graphic granite the quartz is moulded on the crystallised felspar (and in the greater number of granites the felspar is crystallised while the quartz is not), the fluidity whence both have been consolidated cannot have been fusion from heat." "The force of this argument from the crystallisation of felspar in granite

* Illustrations of the Huttonian Theory by Professor Playfair, p. 86.