VIII.

wonderful variety which the direction of the veins and the BOOK forms of the caverns display, the immense heaps of confused and broken substances, the transportation of enormous blocks to a great distance from the mountains of which they appear to have formed a part, every thing, in short, makes us feel, that the history of our globe reaches back to periods far anterior to the existence of the human race, and that the researches which are necessary to bring us acquainted even with the present state of its surface, (and scarcely beyond the surface can we penetrate,) would require a length of time, and an amount of expense hardly to be calculated, before our observations could be so matured and verified as to form the foundations of a complete scientific whole.

Definition of simple aggregate

BOOK IX.

Continuation of the Theory of Geography. Of simple Substances which compose the solid part of the Globe. First Section: Saline, earthy, and inflammable substances.

It belongs to chemistry to examine in what manner the gases, the acids, and the elementary earths, have acted in the formation of the non-organic substances which form the solid crust or surface of our globe, and of which we are now going to consider the external and internal forms. Mineralogy describes, defines, and classifies these substances; geology treats of their origin; but physical geography, the object of which is to investigate the structure, composition, and physical relations of the globe, cannot be accused of going beyond its limits, in tracing out a general view of the various substances of which the solid parts of the earth are formed.

These substances are either simple, that is, formed of the same chemical elements, and having for their nucleus the substances. same integrant molecule; or aggregate, that is, composed of two or more simple substances. The first of these substances are minerals, the objects of the sciences of mineralogy and crystallography; the second are the rocks and earths, which belong to the province of geognosy.

Classifica

nerals.

We distinguish four classes in the mineral kingdom: the tion of mi- first comprehends saline or acidiferous substances, which are composed of an acid united to an earth or an alkali, and sometimes to both. The second contains the earthy substance, into the composition of which earths aloue enter, or sometimes an earth united to an alkali; in the third class are placed all inflammable substances which are

IX.

not metallic; substances hitherto imperfectly analyzed, but BOOK which may be distinguished by the property which they possess, of burning, or of evaporating, when decomposed. The fourth class embraces the metallic substances known by their brilliancy, by their great specific gravity, and, in part, by their ductility and malleability.*

We shall now consider the mineral kingdom, in so far as it regards physical geography, that is, by examining the genera most abundant in nature, and the species most remarkable for their physical qualities. While we take the Terminology of M. Haüy for the basis, we shall compare it with that of other mineralogists.

of lime.

The carbonate of lime, that is, lime combined with car- Carbonate bonic acid, is also called aerated lime, or calcareous spar. It is the most abundant of any known mineral substance on the earth. It belongs to every geological epoch, and to every soil. Among the ancient and primordial masses, it not only forms one of the constituent principles of rocks, but it also is seen in its pure state in immense banks or beds, the peculiar character of which is a laminated or scaly texture, which indicates a confused crystallization. It abounds still more in the secondary or stratified mountains and masses of earth, of which it forms more than the half. It is found also in the third order, combined with clay, and thus constitutes the various marls. It forms also vast beds Talc. in the state of chalk, frequently accompanied by large masses of calcareous shells compressed together, and broken, and which had once been inhabited by marine animals. We are therefore led to consider chalk as a very ancient chemical decomposition of the altered and obliterated remains of shell-fish. It is well known that the madrepores and other polypi of the equatorial seas, form chalk continually in great quantities. The port of Bantam was shut

Hauy, Traité de Minéralogie. Brongniart, Traité Elem. de Minéralogie Delamétherie, &c.

+ Steffen's Memoir upon the Natural History of the Interior of the Globe, p. 26. (In German.)

IX.

BOOK up in less than a century by rocks of coral formed by polypi.* Limestone is discovered mixed with flints and coloured marbles (brèche) in alluvial soils, and also in volcanic soils, where it has been detected by the explosions that have taken place. There are, however, countries where chalk is not found; where, at least, it has hitherto been but very rarely seen; as, for instance, in the neighbourhood of the Cape of Good Hope, and in the granite and volcanic peninsula of Kamtchatka.t

Marble.

Calcareous spar.

The carbonate of lime confusedly crystallized, forms the building materials in France. When it possesses a finer grain, it forms a sort of marble of no great value. According as it becomes harder, and, if we may so express it, more refined, it takes a much finer polish, and is better fitted for the chisel of the sculptor. It is then properly called marble. White statuary marble from Carrara in Italy, is esteemed the purest of any. The coloured marbles are formed of calcareous matter, mixed more or less with extraneous substances. Pliny is right when he says, "Every country possesses its peculiar species of marble." Marbles, however, more regularly crystallized, of a larger grain, and more mixed with particles of pyrites, become more rare as you leave the middle of the temperate zone, and approach the pole.

Crystals of carbonated lime, under the name of calcareous spar, are found in almost every subterraneous cavity, and in all veins. They serve to ornament every cabinet of mineralogy. Filtering through the vaulted roofs of subterranean grottos, this substance forms those concretions Stalactites, known by the name of calcareous stalactites; the various positions and forms of which present all kinds of agreeable and fantastic appearances to the imagination of the specta-. tor. The cagle-stone (géode) is a concretion, the interior

*Blumenbach, Histoire Naturelle, p. 450. Comp. Forster, Péron, &c.

+ Thunberg's Travels, i. 216. (In German.) Sparman's Travels, 142-618. (In German.)

Georgi, Description Physique de la Russie, 1.

BOOK

of which is hollow, sometimes filled up with crystals, sometimes bristled with multitudes of needles. The more abun- IX. dant and uniform calcareous concretion produces those masses known under the name of calcareous alabaster, Calcareous which differs from marble in being less pure, more variegated in its colours, and somewhat more transparent.

alabaster.

tions.

The incrustations which are formed by water, loaded Incrustawith carbonate of lime, have led to the supposition that there are some petrifying springs. These incrustations preserve exactly the figure of the vegetables that have been covered with them, the substance of which has been destroyed. It is in the same manner that the tufas are formed, or calcareous sediments in canals, and the beds of rivers and lakes, the waters of which are charged with this substance.

ated lime.

Other species of lime are of less importance. Some va- Phosphatrieties of phosphated and of fluated lime exhibit coloured ed and flucrystals, which very much resemble the more precious stones, such as chrysolites, emeralds, rubies, and others. Fluated lime is often found in the matter of metallic veins, mixed with the ore.

lime.

Sulphated lime, or lime combined with sulphuric acid, is Sulphated commonly called gypsum, or plaster-stone, when mixed with carbonated lime. When crystallized, it is called selenite. This stone is divisible into brilliant and transparent laminæ, and was used by the ancients instead of glass for windows. It very much resembles the foliated mica, or talc of Muscovy, yet is totally different in regard to the nature of its component parts. The compact sulphated lime, fine and close-grained, and of a beautiful white colour, is the substance which, under the name of gypseous alabaster, or ala- Gypseous bastrite, (pseudo alabaster,) has so often afforded the poets a term of comparison to express the whiteness of the neck or arms: "A skin as alabaster pure." Sulphated lime is often found under the form of hills or little mountains, and sometimes in beds or strata, in countries of the second and third formation. It is doubtful whether there be any of the first formation, or whether the heaps that are known to be among the primitive mountains have not been produced by causes.

alabaster.