the difference of chemical composition, &c. and the Structure the grand characteristic, the Aspect refers to more minute features.

HIS VARIETIES.

The term variety is unobjectionable, as it is equally applicable to objects of animated or inert matter; and diversity may be used to imply a still greater difference than the variety presents. A very faint shade of difference might, if necessary, be called a lineament.

THE WERNERIAN THEORY.

From the sketch imparted by Daubuis son to Brochant, and from Mr. Jameson's Geognosy, we are enabled to form an idea of Mr. Werner's system concern ing the formation of such parts of this planet, as we can hope to observe, little exceeding the three thousandth part of its semi-diameter. I warmly subscribe to the sentiments of admiration which are paid to Mr. Werner's superior talents in many branches of mineralogy, a science infinitely indebted to his industry and sagacity. I also acknowledge the truth of the apophthegm, Natura fecit omnes judices; paucos artifices. But I regret, with his most enlightened admirers, that the scene of his enquiry has been too confined; and that his view of the mountains of Saxony has not been extended over the globe. After forty years of sedulous observation among the Alps, Saussure, who began his labours with a view of forming a system, declares that his hopes were frustrated; and that he had met with such unaccountable confusion that he could not venture to propose a theory, Yet Saussure, to practical observations on a far superior scene, added the advantages of learning, and mathematical and meteorological science, which Mr. Wer her unhappily wants, and which would have corrected and greatly improved his speculations.

Domain I.-Siderous, SIDEGEA, SIDEROUS EARTH. The name sidegca, as not unusual in compounded words, is abbreviated from two Greek terms, signifying iron and earth. The reasons for the introduction of this grand division, adopted in substance by the most eminent geologists, have already been given. Iron acts so important and radical a part in the constitution of our planet, that it deserves to be viewed under various aspects, not only as a metal, but as an earth, strongly

impregnating most of the others, and often exerting a predominating influence. For as, since the recent discoveries, many earths have been known to assume the form of metals, so there can be no impropriety in considering this universal metal under the form of an earth.

When a substance contains more than twenty-five parts in the hundred, or, in other words, one quarter, of iron, it may be worked as a metallic ore, and arranged under that denomination. But in a smaller quantity it will fall under the present division, especially when intimately combined with the other earths. It was by metallogists considered as a calx, or latterly called an oxyd. Mr. Kirwan, who has rightly added calces of iron to his description of the earths, says, that they are formed of that metal, com. bined with different proportions of pure air, and frequently of water also and fixed air.

"One hundred parts metallic iron are capable of taking up 66 or 70 of pure air. When 100 parts iron contain but 40 of this air, the compound is still magwetic. His table of the fusibility of the simple earths presents some curious experiments on the mixture of calcined iron and rust of iron, with other substance, which show the power of this metal. Even when it only amounts to four parts in the hundred, it sensibly influences the compound.

Sidegea, or siderous earth, is so gene rally diffused, that almost every mineral substance derives its colour from it, from a pale blue to the deepest red. Animal substances contain it; and it exists in the vegetable kingdom, even in plants apparently supported merely by air and water. It would appear that even the atmosphere abounds with atoms of iron, whence perhaps the meteoric stones.

Domain II.-Siliceous. SILEX, SILICA, OR SILICEOUS EARTH.

This earth derives its name from the silex, or flint, in which it abounds. Some also denominate it quartzose earth, because it is perhaps more abundant in the stone called quartz, which, when trans. parent and crystallized, is styled rock crystal. It so frequently occurs in the form of sand, which covers a great part of the globe, either alone or mixed with clay, that late chemists infer that such sand arises not only from the decompo sition of rocks, but is often a disturbed or hasty crystallization of silica. This is further confirmed by the circumstance

pre

The carbonic acid gas, more briefly called carbonic acid, forms a constituent part of the atmosphere, in the proportion of about 1, in the 100, while the remainder consists of about 77 of nitrogen and 22 of oxygen gas. Combined with the earths, it forms carbonates; and that widely extended substance called limestone, which is often primeval, is a carbonate of lime.

"Carbon itself not only appears in the purest state in the diamond; but forms the preponderant part, sometimes even 90 in 100 of the substances now under view, and which have therefore been called carbonaceous. They not only enter into the composition of rocks, and some even of the primitive, but form rocks themselves, as coal has been found in masses of 80 or 90 feet in thickness. The trivial name of sea-coal, arising from its importation at London, might there fore well be exchanged for that of rock coal, as we say rock-salt. Some might, perhaps, prefer the German appellation of bergarts, implying substances of whatever kind which enter into the composition of mountains; or the Greek geostromes, proposed by Patrin, to denote the strata of the earth. But as the conchitic beds of limestone, sometimes more recent than coal itself, though often in thin strata, universally assume the name of rocks, any refined discrimination would appear unnecessary. It has already been more than once observed that the division of mineralogy into three quite distinct and separate provinces, METALLOGY, LITHOLOGY, and PETRALOSY, would be of the utmost importance

to the progress, illustration, and utility of the science; each of them being amply sufficient for the life and labours of one man; and, in this case, the subjects onder view could not be allotted to any other grand division.

Domain VII.-Composite.

This division comprehends the rocks which consist of different substances blended together, and for which no distinct denominations have been adopted. Many of them have been classed under vague names, particularly that of gra

nite.

Under the division of Aggregated Rocks, Gmelin, in his edition of Linnæus, has arranged granite, gneiss, por phyry, amygdalite, bricia, and sandstone; and the reader will be surprised to find what various and discordant objects are united under these vague appellations. Mr. Kirwan has, in like manner, two titles of Aggregated and Derivative Stones; the other rocks heing considered under the simple substances.

The latter six great divisions of the rocks, being derived, not from the nature of the substances themselves, but from accidences or circumstances, may be called ACCIDENTIAL, or circumstan tial; while the former divisions are SUBSTANTIAL. The chemical Mode therefore, so essential in the substantial ranks, here becomes foreign to the object; and the terms Structure and Aspect, derived from the self-apparent nature of the stones themselves, would become yet more improper, as by far the greater part of these rocks are even compounded of various domains, united in one mass.

The term DOMAIN has been retained, not in its former acceptation, which may strictly imply the preponderance or predominance of a particular earth or substance; but, in a more general sense, equally applicable to all the twelve divisions; that is, merely a continuation of the metaphoric language of the Mineral Kingdom, Provinces, and Domains. In this sense it is indeed chiefly used in the first six divisions; the other implication, of predominance or preponderance, be ing of a secondary and subsidiary nature, and only a further recommendation of its propriety.

But the term Mode implying the che mical mode of combination, which is even more essential than the nature and power of the substances combined, as appears from an infinite number of analyses, it cannot be admitted into these

new divisions, derived from accidential, and not from substantial, differences, as has been just mentioned; and, the inferior terms being equally objectionable, the adoption of a new appellation be. comes indispensable. The word Nome has been adopted, as short and convenient, and as applied by the Greek writers to the districts of Egypt, the first country where chemistry and mineralogy appear to have been studied. It is therefore not only of classical authority, but has an affinity, so to speak, with the parent country of the science, and thus presents scientific recollections. The author has the greatest aversion to unDecessary neology, the chief use of language being to be understood, and that the thoughts may be accurately perceived, as flowers or fruits in a vase of crystal; but, when a science has assumed a new aspect, like chemistry, or is wholly new, like mineralogy, new words become indispensable to express new ideas.

For the sake of memory, and easy reference, the latter divisions follow the general succession of substances in the former; but this arrangement must not be understood to imply that any substance is predominant, as either may have greater or less importance in differ ent parts of the same rock. After these considerations, the proper arrangement of the Composite Rocks will not be at tended with much difficulty.

Domain VIII-Diamictonic. These rocks, in which the substances may be said to be chemically combined, form the most difficult province of the whole science, and might deserve a separate treatise like the Cryptogamia of the Botanists. Siderous earth, for example, may be found so intimately and equally combined with the siliceous, that the rock cannot with propriety be ar ranged under either. The celebrated glazed rock, which Saussure observed near the monastery of St. Bernard, is of this description; and there is a specimen in the author's collection. It has been called an intimate combination of quartz and roche de corne,

Most of the Derivative rocks of Kirwan belong to this Domain. The name and idea he is said to have borrowed from Bergman. The aggregated stones of Kirwan comprehend granite, gneiss, porphyry, amygdalite, sand-stone, and other substances, visibly compounded of various materials; while his derivative

stones he distinguishes from aggregates by this, "that the associated ingredients are not visibly distinct, or at least require microscopes to render them so.” He adds, that a derivative stone may be denominated from the species (that is, the Mode), which still predominates; but, if it participate equally of both, it may receive its denomination from ei ther. The siderous, siliceous, and argillaceous earths, forin the most frequent combinations; while those of calcareous earth and magnesia are far more rare. In his Geological Essays he observes, that stones are either original, as granite, or derivative, as sand-stoné; while, in his Mineralogy, he has classed sandstone, along with granite, among the ag. gregates.

The appellation and distinction are in fact alike fallacious. That a red sandstone may be derived from the detritus of a red granite, may be justly admitted; but this affords almost the only example of a real derivative stone. And the intimate combinations of which Mr. Kirwan speaks are so far from being derivative, that they often belong to the most original and primitive substances. But, when Mr. Kirwan published his valuable system in 1794 (and the last edition is merely reprinted), the knowledge of rocks was extremely confined, and regarded only as an appendage to mineralogy, instead of forming a grand and distinct science, a rank to which its dignity and importance authorise it to as pire.

The terin Diamictonic, derived from the Greek, implies that two or more substances are so thoroughly mingled, or, in the language of chemistry, so intimately combined, that the rocks can not be arranged under either D›main, either from preponderance or predomi

nance.

in speaking of a Russian traveller, says, that he would have boldly asserted that a roasting goose graduates into the spit. Thus some theorists have conceived that lime becomes flint, or flint graduates into line, from the mere mixture of the particies near the line of their junction. The most proper and undoubted gradua tions occur only among the kindred rocks; and are generally a mere variation of the mode or structure; as the passage from granite to gneiss, or from grauite to granitic porphyry. If the granite be surcharged with siderite, and its particles become very sinall, it may pass into the real basalt of the ancients; but can never become a basaltin interspersed with chysolite or zeolite; and if the basaltin occur with granite, it must be merely adherent. Keralite may, by im. bibing iron from the atmospheric air, or whatever cause, become jasper. Wer. ner has observed, that wacken passes into clay on one hand, and basaltin on the other; which last again passes into basalton or grunstein. Many other undoubted transitions may be observed; but it will suffice to enumerate some of the most remarkable, leaving the others to time and accurate observation.

Domain XI.-Decomposed.

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while in other spots the black oxyd may predominate. Argillaceous earth found in the most primitive substances; and theory can scarcely be expected to determine whether the fertile clay, which forms so prodigious and important a portion of the surface of this globe, and furnishes aliment to animals and vegetables, arises from a decomposition etfected, during myriads of ages, by the superincumbent waters; or by a mere deposition from the original mass aud constitution of the waters themselves.

The decomposition of rocks forms a striking feature in geology, as a great part of the productive soil, and many of the substances used in important manufactories, may be considered as chiefly derived from this circumstance. Several of the most useful clays are reputed by some to be merely decompositions of felspar; the mixture of sand being a decomposition of quartz. Bergman found the loam near London, to contain only 13 of argil; the remaining 87 being a redish grey sand, as fine as flour. What is called mould, consists chiefly of vegetable and animal remains. The fall of leaves in a forest creates a fine black mould.

On the decomposition of rocks, the observations of a skilful chemist must be particularly exact and interesting, for which reason those of Mr. Kirwan are extracted; more especially as they abound with examples which are essential to the nature of the present work. It may also be prefaced, that the decomposed rocks have never hitherto been treated in any professed work of mineralogy, so that the novelty of the subject calls for every aid of illustration,

The decomposition of rocks is not only a curious subject in itself, but of the greatest importance to the arts, particularly architecture and sculpture. Many noble edifices have soon become disfigured, because the architect did not know the easy decomposition of the materials. Thus at Trianon the pillars are already decayed, because the argillaceous nature of the marble of Campan will not bear exposure in the open air, where it soon exfoliates. At Oxford it has been observed that some of the public buildings are injured, because the builders had not studied the nature of the stone, which requires to be laid in its original position in the quarry, that the first compression may still exist, as otherwise it will imbibe the moisture, and thus split or crumble in frosty weather. Sculptors are singularly anxious that the stone which they use should not be subject to this defect; and their example should be followed by architects, as the duration of their works and reputation depends entirely on this branch of knowledge. It would appear that the ancients, who always mingled the useful with the ornamental, had particularly investigated this subject, even in very early times; for the Egyptians, in their eternal monuments, had already learned to prefer granite and porphyry, the two most durable substances in nature; and which have the additional advantage that they afford no temptation for destruction, because they cannot, like marble, be cop

In various parts of England, and other countries, the loam is of a red colour, and proceeds in what may be called belts or zones (for strata can only be superimposed on each other) for a great distance, but with various interruptions, This red tinge can scarcely arise from the decomposed felspar of red primeval granite, as some have supposed; for in that case the hardest nodules of the granite would probably still be found, as in the red sand-stone; but may merely proceed from the admixture of red oxyd of iron, 4

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