Imágenes de páginas
PDF
EPUB

Genus 2d. With a base of Mica.
2. Gneiss, - this division contains a very imperfect list of

varieties.
3. Mica Schist,, one of the enumerated varieties is a gneiss.

Genus 3d. With a base of Schist, (Clay slate.)
Sp. 1. Phyllade, - includes many varieties of argillaceous schist

micaceous, or containing imbedded minerals, and even bituminous marl slate it appears also to contain a variety of gneiss, and some

graywackés. 2. Calschiste, - a mixture of clay slate and carbonat of lime.

Genus 4th. Base of Talc. sp. 1. Steaschiste, - includes talc slate and chlorite slate, together

with many other compound substanees.

Genus 5th. Base of Serpentine. Sp. 1. Ophiolite, - serpentines which contain imbedded minerals. .

We cannot help remarking, that as well in this case as that of the phyllade, we have a striking example of the great inconvenience of a system which separates the simple from the compound rocks; and from a circumstance so, unimportant, in the case of serpentine, as its occasionally containing chromat of iron, or garnets.

Genus 6th. Base of Carbonat of Lime. Sp. 1. Cipolino, - limestone containing mica.

2. Oficalce, - limestone containing serpentine, &c.

3. Calciphyre, – limestone containing various imbedded minerals. We cannot see that any of these incidental varieties have a claim to the title of species; nor is the division even consistent with itself; as the presence of garnet, hornblende, or augit, might as well confer on the varieties of the 3d Sp. the rank of separate species,

Genus 7. Base of Cornénenne. (this is very indefinite.) Sp. 1. Variolite, - certain amygdaloids. 2. Vakite, - other amygdaloids.

Genus 8. Base of Amphibole. Sp. ). Amphibolitę,- a sweeping term, which comprises many differ

ent rocks, in which either hornblende or

actinolite enter as ingredients. 2. Basanite, - this also appears intended to comprise every

rock which has a base of basalt, 3. Trappite, - roches de trapp—we quote the author in the

original, as we can form no definite idea of this species ; and as little, we may add, af the former.

4. Melaphyre, - certain varieties of dark-coloured porphyry.

Genus 9. Base of Amphibolic Petrosilex. This base is not very intelligible—is it a basalt or a dark clinkstone ? Sp. 1. Porphyry, - the last species has a base of amphibole pe

trosiliceux,' and in these varieties the base is ' petrosilex amphiboleux;'-a distinction

too refined for our state of information. 2. Ophite, - green porphyry-surely no more than a variety

of the last species. 3. Amygdaloide,-including the variolites of Durance, and the

orbicular porphyry of Corsica—it also com-
prises some more porphyries, we do not see

why.
4. Euphotide, - Verde di Corsica.

Genus 10. Base of Petrosilex, or of Granular Felspar.
We do not comprehend how these two substances can mean the
same thing.
Sp. 1. Eurite, - including whitestone (weiss-stein), clinkstone,

some clinkstone porphyries (again), and floetz

trap porphyries--a very strange association. 2. Leptinite, - more weiss-stein—and apparently some gra

nites-(hornfels.) 3. Trachyte, - more porphyries with base of petrosilex. We confess that all this appears to us very disorderly.

Genus 11. Base of Argilolite. Sp. 1. Argilophyre,- claystone porphyry. 2. Domite, - claystone with mica.

Genus 12. Base of Pitchstone or Obsidian. Surely so excellent a mineralogist does not mean to confound these two substances. Sp. 1. Stigmite, - pitchstone or obsidian porphyry.

Genus 13. Base indeterminate. Sp. l. Lava, - lavas and scoriæ simple and compound a very

short process for disposing of the volcanic rocks.

Class III. AGGREGATE Rocks.

Genus 1. Cemented. Sp. 1. Psummite, - appears to contain quartz rocks, micaceous sand

stones, graywackés, and graywacké schists ; and is evidently, even in a mineralogical view, very injudiciously contrived.

Genus 2. Imbedded.
Sp. 1. Mimophyre,- more sandstones and graywackés.

2. Psefite, - some of the old red sandstones.
3. Poudingue, - this appears to comprise a great variety of

rocks-some of them local, and others ap

pertaining to the former. 4. Breccia, - these are to be distinguished by the angularity

of the fragments.

It is abundantly evident that this arrangement is totally unfit for the purposes of geological description; but it is unnecessary to point out the causes, since they must be obvious to the most ignorant of our readers. The respect which we entertain for the author prevents us from noticing more of its defects as a mineralogical arrangement. We cannot either see the necessity or the propriety of the Neology which he has thought fit to adopt; but it is unnecessary to say more on the subject, as this system seems to have attracted little attention, though published in the Annales de Chimie; (from which work we have taken our abstract), as long ago as the year 1813.

The author next in the order of the Essays is De la Métherie; and his arrangement is preceded by a theory, which, as we do not very well understand it, we shall not attempt to analyze.

His system does not admit of a brief analysis, like the former; and moreover it is not deserving of one. We shall content ourselves therefore with a mere sketch of his plan.

It consists of three grand divisions; the aggregate crystallized, imbedded, and agglutinated. The two latter are again divided into primary, secondary, alluvial, and volcanic.

Under the First Division are twelve subdivisions--the quartzose,--argillaceous,—magnesian,-calcareous,--barytic,-strontianic,-zirconic;-glucinic,- gadolinic,- sulfurous,-combustible,-and metallic: all of these being supposed to form so many classes of aggregate rocks; a very latitudinarian use certainly of that term. In some of these subdivisions are to be found, as might be expected, the well known rocks, such as granite, gneiss, &c. in all the diversity of species and varieties; capriciously enough divided, but all apparently described from actual specimens. This is all very well; but they are accompanied by others, which are either accidental mixtures of minerals, and not rocks at all, or, what is worse, are purely imaginary. From this determination to fill up a visionary plan, we have such rocks, for example, as barytes and fluor spar, strontian and galena, emerald and granite, sulphur and gypsum, anthracite and granite, gold and quartz, and so forth. This, we must say, is egregious trifling.

In the Second Division there are the same twelve subdivisions. But here, as might be expected from thus hunting down his system, the author gets into much greater absurdities, attended by no small confusion. The paste of the quartzose subdivision may be either quartzose, or argillaceous, or magnesian, or calcareous, or barytic. Or else it may be Keralic, or Petrosiliceous, or Tefrinic, or Leucostic, or Ophitic, or Variolitic, or Cornean, or a compound of many rocks. The imbedded substance may also consist of any siliceous mineral. So much for the felicity of this arrangement; to say nothing of these unnecessary terms, each of which would require a definition of its own, Let us see the result-the way in which all this order is applied to practice,

Under the Quartzose subdivision stands first the genus Porphyry, containing eleven species, besides varieties: to which are added the Decomposed porphyries, containing, among other matters, the claystore porphyry of Werner, which is certainly not a decomposed rock. Next comes the genus Amygdaloid, comprising however but two of the numerous varieties of this modification; namely, those which contain agates, and those which contain calcareous spar. The remainder appear to have been forgotten. The third genus is Variolite; containing five species, of which one is the orbicular granite of Corsica; another, clay slate, with occasional crystals of hornblende; another, mica slate, with similar crystals. This may be an arrangement in words, but it is surely nothing more. In the fourth genus we find amygdaloidal porphyries, with an imperfect enumeration of varieties under the name of Species.

. After this follows a sort of episodic division, consisting of Porphyroids of primary formation-rocks which do not contain felspar. Such are, quartz and tourmalin, quartz and garnet, quartz and titanite, argillaceous schist and hornblende (the second time), the same and mica, the same and octoedral iron, mica schist and garnet, mica schist and hornblende (again), talc and bitterspar, steatite and tourmalin, chlorite schist and tourmalin, serpentine and oxidulous iron; together with many other similar compounds, all formally displayed under tặe requisite subdivisions, genera, species, and varieties. If this be an arrangement, we know not that any other division than Porphyroids would have been required; as it might, on the same principle, comprise every compound rock; and many things besides.

After all this (and we have been so confused with Divisions

and Subdivisions that the whole plan of the arrangement vanishes from cur eyes), comes a First Section on the Breccias of primary formation ; a second on Poudingues of the same na-, ture, and a third on Grits; – which ends this strange eventful classification. Each of these contains, of course, the faa. vourite twelve subdivisions already enumerated; although the author has been mightily puzzled to fiii them, if we may judge by such ingredients as the following-a strontianic Leccia, a zirconic breccia, a metallic breccia, and so forth. To be sure, he has the candour to acknowledge that some of these, such as a breccia composed of yttria cemented by yttria, or gadolinic yttria,' has never yet been found; and, we may add, never will.

But it is fruitless to examine further into this scene of confusion, which, under all the parade of logical arrangement, describes imaginary substances, and omits existing ones; confusing pretty nearly all the rest in such a manner as almost to dely the powers of analysis. Pinkerton was at least amusing.

The arrangement of Signior Tondi being a geological one, it is necessary to give a somewhat fuller account of it than of the last; and to enumerate the geological distinctions on which he thinks proper to found it.

He divides his rocks into masses, beds, transition rocks, stratified rocks (foetz), alluvial, and volcanic, substances. This distinction is Wernerian, and to a certain degree theoretical ; and, as will be seen, it is productive of no small confusion.

The first class, that of the massive rocks, consists only of granite (that containing mica), which is exclusively called primary.

The next, consisting of bedded racks, contains secondary granite (how is this ascertained ?) as the first species. Subordinate to this are, quartz rock,-graphic granite, -mica,-compact felspar,---and speckstein. Now, quartz rock is found in enormous strata, and is assuredly not subordinate to any granite; graphic granite again is always found in veins; compact felspar occurs either in veins or large nodular masses; and mica is not a rock at all. Here therefore is a geological arrangement, if it can be called such, deficient in the first and essential principle of geological knowledge.

The second species in this class is weiss-stein, which might with more propriety have been placed under the versatile term subordinate; like many others which, with less propriety, have found their way into this convenient repository of ignorance, Gneiss and Syenite are made subordinate to this species; but, inmediately after, gneiss constitutes a species of itself; having,

« AnteriorContinuar »