Page images

of the views of the author respecting the places which they occupy in the structure of the earth, and the analogies by which they are mutually related.

Having thus stated the arguments and objections that seem of chief importance in this dispute, and, as we trust, shown sufficient cause for preferring the geological method of arrangement, we shall give a brief sketch of the classifications of the four authors in the Essay under review. The disadvantages of a mineralogical arrangement, for the purposes of geological science, will thus become practically apparent on the one hand; although, on the other, it will be seen that the two last authors, treading in the antiquated steps of their master, instead of following the path of Nature, have left us nothing but the shadow of a hypothetical classification.

The superiority of Brongniart's work, no less than the reputation of its author, induces us to give his classification complete, but in the briefest abstract which we can make. The others must be passed over more hastily. We have not room to indulge in many remarks, nor will they be necessary to the geological reader: a few will suffice to point out the places of the more prominent defects. We shall translate the foreign terms that may be required into the synonimes most in use; but we have too little confidence in the eventual adoption of the author's neology, to think it necessary to give an English physiognomy to the Gallicized Greek compounds in which he deals. The brief form into which this arrangement is here condensed, will render its defects much more apparent than they are in the original.


Sp. 1. Granite,

2. Protogine, 3. Pegmatite, 4. Mimose,

Sp. 1. Syenite,

2. Diabase,

[ocr errors]

[ocr errors]

Genus 1st. Felspathic.

common granite, with mica only.

the same, containing steatite, talc, or chlorite. graphic granite.

- a compound of pyroxene and felspar.

[ocr errors]

Genus 2d. Amphibolic.

granite containing hornblende-hornblende schist containing felspar, &c.

greenstone-hornblende schist containing fel

spar-greenstone porphyry-orbicular granite of Corsica.

3. Hemithrene,- a hornblende rock containing carbonat of lime.. CLASS II. CRYSTALLIZED ROCKS. (ANISOMERES.)

Genus 1st. With a base of Hyaline Quartz.

[blocks in formation]

quartz and mica-probably a variety of quartz rock,

2. Gneiss,

Genus 2d. With a base of Mica.

3. Mica Schist,Genus 3d.

Sp. 1. Phyllade,

2. Calschiste,

[ocr errors]

this division contains a very imperfect list of

one of the enumerated varieties is a gneiss.
With a base of Schist, (Clay slate.)
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

- 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.

Sp. 1. Ophiolite,

Genus 5th. Base of Serpentine.

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,
2. Oficalce,
3. Calciphyre,

- limestone containing mica.

- limestone containing serpentine, &c.

[ocr errors]

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,

2. Vakite,

certain amygdaloids.

- other amygdaloids.

Genus 8. Base of Amphibole.

Sp. 1. Amphibolite,- a sweeping term, which comprises many differ

[blocks in formation]

ent rocks, in which either hornblende or actinolite enter as ingredients.

this also appears intended to comprise every rock which has a base of basalt,

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, of the former.

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

Genus 9. Base of Amphibolic Petrosilex.

[ocr errors]

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 petrosiliceux,' and in these varieties the base is petrosilex amphiboleux; '-a distinction too refined for our state of information. green porphyry-surely no more than a variety of the last species.

2. Ophite,

3. Amygdaloide,-including the variolites of Durance, and the orbicular porphyry of Corsica-it also comprises 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,

2. Leptinite,

3. Trachyte,

including whitestone (weiss-stein), clinkstone,

some clinkstone porphyrics (again), and floetztrap porphyries-a very strange association. more weiss-stein-and apparently some granites (hornfels.)

- 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,

Sp. 1. Lava,

- pitchstone or obsidian porphyry.

Genus 13. Base indeterminate.

lavas and scoriæ simple and compound-a very short process for disposing of the volcanic rocks.


[merged small][ocr errors]


Genus 1. Cemented.

appears to contain quartz rocks, micaceous sandstones, graywackes, and graywacké schists; and is evidently, even in a mineralogical view, very injudiciously contrived.

Sp. 1. Mimophyre, 2. Psefite,

3. Poudingue,

4. Breccia,

Genus 2. Imbedded.

more sandstones and graywackés.
some of the old red sandstones.

this appears to comprise a great variety of rocks-some of them local, and others appertaining to the former.

- 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 gyp

sum, 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 claystone 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 the 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

« PreviousContinue »