COMPOUND MINERALS,
OR
ROCKS.
249. There exist considerable masses of minerals in a state of combination, or aggregation with each other. These constitute the rocks and soil of which the globe of the earth is composed; and the study of them is called GEOLOGY. The opinions of learned men relative to their structure, and original formation, have produced various systems denominated theories of the earth; but, when we consider that the greatest depth beneath the surface to which the art and industry of man have been able to penetrate, does not exceed 1/35000 part of the earth’s diameter, we must confess that this is very insufficient to allow of any correct opinion being thereby formed concerning the structure of the whole.
Modern geologists, for the more convenient arrangement of the compound minerals, have divided them into four classes, which they denominate primitive rocks, secondary rocks, alluvial depositions, and volcanic rocks.
I. PRIMITIVE ROCKS.
250. These are so called from their being considered by geologists, to belong to the first formed parts of the globe.
Rocks of this description are of a nature extremely hard. They contain no vestiges whatever of animal or organic remains; and the substances of which they are composed are crystallized. They rise through other rocks at various elevations, in every quarter of the globe; and never either alternate with, or rest upon rocks that enclose organic remains, though they are themselves frequently covered by such.
The following are the principal kinds.
251. GRANITE or moonstone is a compound rock composed of felspar ([110]), quartz ([76]), and mica ([123]), each in crystalline grains of various size, and promiscuously arranged; sometimes one and sometimes the other of these ingredients predominates, but generally the felspar.
This is one of the most common and most widely extended rocks that are known; and is considered as the foundation on which the secondary rocks are deposited. In Cornwall it is very abundant, and veins both of copper and tin are found in it. Granite forms the summits of the highest mountains in Scotland, of the highest of the Grampian Hills, the Alps, and the Pyrenees; and indeed the loftiest parts of most of the countries of the world. The Logan or rocking stones, in Cornwall, are immense blocks of granite.
The uses of this stone are numerous and important. Millstones, steps, troughs for stamping mills, and innumerable other articles, are made of it. The streets of London are chiefly paved with granite, and its hardness and durability render it peculiarly eligible for this use. Weather has little effect upon it. Consequently, when applied to architectural purposes it is found infinitely preferable to Portland stone, of which nearly all the public buildings of modern date in London have been constructed, and many of which are fast going to decay. This circumstance induced the proprietors of the Waterloo Bridge to adopt granite in the construction of that edifice. Mr. Smeaton also chose it for the outer walls of the Eddystone Lighthouse.
252. Scottish Granite.—Scotland is remarkable for many kinds of granite, some of which are susceptible of an excellent polish. The greatest part of the mountain of Ben Nevis, near Fort William, is composed of a reddish granite, one of the best and most beautiful that is known. This mountain is nearly a mile in perpendicular height, and is said to contain granite enough for all the kingdoms of the earth, although they should be as partial to this stone as the ancient Egyptians were. Columns and obelisks of any size and height might be cut from it: for the rock is one uniform mass, without appearance of strata, division, or fissure of any kind. A convincing proof has been given of the strength and hardness of this granite, in a fragment of several tons’ weight, which fell from nearly the top of a precipice five hundred yards in height, upon a hard and solid rock below, and yet continued entire.
253. Granite of Ingria.—A beautiful red granite is found in some parts of Russia, remarkable on account of the felspar ([110]) that it contains, appearing in round or oval pieces, from half an inch to two inches in diameter. This granite, when polished, exhibits shining spots of round or oval shape, which give to it somewhat the appearance of being studded with precious stones.
The royal summer garden at Petersburg is decorated with a superb colonnade of Ingrian granite. The columns are sixty in number, and each of a single piece twenty feet high, and three feet in diameter. Many of the public buildings in Petersburg are of this granite. An immense block of it thirty-two feet long, twenty-one feet broad, and seventeen feet high, forms the pedestal of the celebrated equestrian statue of Peter the Great, in that city.
254. Graphic Granite.—A singular kind of granite has been discovered in the island of Corsica, and lately near Portsoy in the north of Scotland. The ground of this granite is a whitish or reddish yellow felspar, in which are embedded crystals of quartz each from an inch to an inch and half long, and several lines in diameter. The name of graphic granite was given to it in consequence of an imaginary resemblance which the sections of these crystals have to Hebrew, or Arabic, and sometimes to musical characters.
255. GNEISS is a primitive rock, consisting, like granite, of felspar ([110]), quartz ([76]), and mica ([123]), but differing from that rock in its structure, being slaty.
Mountains of gneiss are not so steep as those of granite, and their summits are usually rounded. Ben Lomond and others in Scotland, and mount Rosa in Italy, are almost wholly of gneiss, as well as the middle part of the Pyrenees. It is not an uncommon rock, but in Britain is of less frequent occurrence than granite.
Many valuable metallic ores are found in veins of gneiss. This rock also sometimes contains crystals of garnet ([70]), and tourmaline ([69]).
256. MICA SLATE, or MICACEOUS SCHISTUS, is a primitive rock of slaty structure, consisting principally of quartz ([76]) and mica ([123]).
Like gneiss, it is rich in ores. It often contains beds of magnetic ironstone ([235]), galena ([239]), copper, blende ([241]), cinnabar ([228]), and sometimes even gold. It frequently has garnets, and sometimes tourmalines ([69]), interspersed in different parts of it.
Mica slate occurs in many parts of Scotland; the mountain of Schehallien, and the rocky adjacent country, are in a great degree composed of it.
257. CLAY SLATE is a primitive rock generally of dull blue colour, more or less compact, always slaty, and always stratified.
Under the appellation of clay slate are included roofing slate ([120]), whet slate ([122]), drawing slate ([121]), and some other kinds already described.
Few rocks abound more in veins and beds of valuable metals than slate. In different countries it contains ores of tin, lead, cobalt ([247]), silver, and copper; and gold, and mercury ([228]) sometimes occur in it. The celebrated quicksilver mines of Idria ([228]), and the immense mass of copper at Parys mountain in the island of Anglesea ([230]), are in clay slate. Crystals of pyrites ([236]), and sometimes garnets ([70]), and thin layers of quartz ([76]), and felspar ([110]), are all occasionally found embedded in it.
This is a widely-extended rock; it sometimes forms whole mountains, and even chains of mountains; but these usually have a gentle acclivity. The summit of the celebrated mountain called Skiddaw in Cumberland is of clay slate.
258. PRIMITIVE LIMESTONE is a simple mountain rock of crystalline or granular structure; and generally of white, yellowish, greenish, or reddish colour.
To this species of rock belong many of the rich and beautiful kinds of marble already described (143, &c.). Carrara, or statuary marble ([146]), is a familiar instance of it. Whole mountains in Stiria, Carinthia, Carniola, and the Pyrenees, and three mountains in Switzerland, 10,000 feet in height, are of primitive limestone. The mountain of Filabres in Spain, is said to consist of one block of white granular marble, 2,000 feet high, and three miles in circuit; without intermixture of other earths or stones, and almost without a fissure.
Various mineral ores, in beds and veins, as lead, zinc ([241]), and iron, are occasionally found in this kind of rock.
259. PRIMITIVE TRAP is a mountain rock composed of a black mineral called hornblende, mixed, in some varieties, with felspar ([110]), and, in others, with mica ([123]).
The word trap is of German origin, signifying a stair; and rocks of this formation are called trap rocks, because their strata, when exposed, usually jut out, one beneath the other, somewhat like a stair. Under this term is comprehended a series of rocks, distinguished chiefly by the hornblende, which they all contain.
Rocks belonging to this formation are numerous. They occur in Scotland; and abundantly in Derbyshire and some other parts of England. In many countries they constitute considerable hills. They abound in ores.
260. SERPENTINE is a primitive rock, usually consisting of quartz ([76]), magnesia ([198]), alumine ([197]), with a portion of oxide ([21]) of iron.
This rock and its various uses, have been already described ([132]). It generally occurs in shapeless masses and beds; and seldom in distinct strata. It is found in Cornwall, the island of Anglesea, and several parts of Scotland; but it rarely forms mountains.
Ores of lead, silver, and copper, are sometimes found in serpentine.
261. PORPHYRY is a primitive rock, consisting of quartz ([76]) or felspar ([110]), or both, embedded in a solid and compact cement or ground.
The ground or basis of porphyry varies in the different kinds. In some it is claystone, in others pitchstone, hornstone, or compact felspar.
When not covered by other formations, porphyry sometimes forms single rocks; but it never constitutes elevated mountains. It occurs in beds of considerable magnitude, but never appears in distinct and well-defined strata.
There are many beautiful and splendid works in porphyry. Obelisks, statues, and columns, wrought in it, have had great celebrity. It is susceptible of a polish as high as that of marble, but is so hard, that the expense of working it has caused it to be much neglected by the moderns. This hardness, however, renders it very durable, and also constitutes it a material of great utility for mortars, slabs for grinding colours upon, and for several other purposes.
Porphyry was much esteemed by the ancient Egyptians; and Pliny informs us that the procurator-general in Egypt, under Claudius Cæsar, brought thence, for that Emperor, certain statues of porphyry, which he conceived to be very valuable: this act, however, was not much approved, and the example was not followed by any other Roman.
The principal quarries of porphyry are in Egypt; but this stone is also found in Italy, Germany, and various parts of the European continent. It may be traced from Norway to the borders of the Black Sea, and it has been discovered in some of the western and northern parts of Great Britain.
262. SIENITE is a rock composed chiefly of felspar ([110]) and hornblende. Its colours are usually reddish and black.
Some varieties of it contain quartz ([76]) and mica ([123]), with but little hornblende. In these the colours are various.
Although this is a less abundant rock than any of those that have yet been mentioned, it occurs, in great abundance, at Mount Mado, in the island of Jersey. There are extensive quarries of it in that mountain, not only for the use of the island, but for exportation to England, and other distant countries. The cliffs, for a long space, and an elevation of a hundred feet or more, consist entirely of sienite, in large masses, which are apparently uninterrupted by a single fissure. Shafts for columns of considerable length have been taken from these quarries; and, were the demand sufficient to call for new openings, it is imagined that columns of twenty feet and upwards in length might be raised. The felspar is of a flesh colour, and the stone is capable of a beautiful polish.
A somewhat similar kind of sienite is found at Grande Roque, in the island of Guernsey, in large masses, which are quarried for building stones. Sienite also occurs in some parts of Scotland and Derbyshire; in Saxony, Hungary, the island of Cyprus, and Egypt. Its name has been derived from that of the city of Syene, in Upper Egypt, where it is found in great abundance.
Sienite was much used by the ancients in ornamental architecture. What was called the red granite of Egypt (for this rock has usually been considered a granite) furnished numerous magnificent obelisks and columns, of a single piece, which have been much admired in Rome and other places. The ancient artists sometimes cut this kind of stone into statues, vases, monumental and other works. The celebrated column in Egypt, upwards of ninety feet high, and known by the name of Pompey’s Pillar, is formed of sienite.
In veins of this rock are found, in different countries, many kinds of metallic ores: among others, silver, iron, tin, copper, and lead.
263. QUARTZ ROCK is a simple mountain rock, usually of granular texture, and whitish colour.
It sometimes contains mica, in which case it has a slaty form.
In certain mountains of Scotland, and the Scottish islands, quartz rock is very abundant. On the Continent it appears in Saxony, Bohemia, Silesia, and several other countries. We are informed that a mountain, 350 feet high, and near 5000 feet broad and long, one of the Altaisch chain, in Siberia, consists entirely of a milk-white quartz.
The uses of quartz have been already described (76, &c.) This kind of rock does not contain metallic ores of any description.
II. SECONDARY ROCKS.
264. Secondary Rocks are composed of, or at least contain within them, the mineralized remains of organic substances. These must necessarily have been formed at a period subsequent to the formation of those organized bodies the remains of which they enclose; and they have apparently been formed by the deposition of water. Hence it is that, to distinguish them from rocks of the preceding class, they have received the appellation of secondary. They always rest upon or cover primitive mountains, and sometimes lean upon their sides or invest them.
Werner, the celebrated German mineralogist, makes two divisions of secondary rocks. The first of these he denominates transition rocks, and states that they are less perfectly crystallized than the primitive rocks; and that they enclose the remains of marine animals, no species of which are at this time known to exist: the other division he terms floetz, or flat rocks, because they are generally disposed in horizontal or flat strata. Some of the latter contain the fossil remains of marine animals and shells, approaching in character and appearance to the kinds which are now found in the ocean; and others contain shells precisely similar to those now known to exist. These rocks usually occur at the foot of primitive mountains, or in deep valleys.
1. TRANSITION ROCKS.
265. TRANSITION LIMESTONE is distinguished by containing marine petrifactions of corals, and other zoophytes which are supposed no longer to exist. It often contains veins of calcareous spar, and exhibits a variety of colours, which give to it a marbled appearance.
This species of limestone occurs in immense beds, and forms a great portion of the mountainous parts of Derbyshire and Scotland; but it does not rise so high, on the sides of mountains, as primitive rocks ([250]).
It often contains veins of valuable metallic ores. When cut and polished, many of the varieties of transition limestone are beautiful marbles; some of them have been already described.
266. GREY WACKA is a transition rock, composed of pieces of quartz ([76]), flinty slate, felspar ([110]), and clay slate ([120]), cemented together by a basis of clay slate.
It has various appearances, the pieces being sometimes as large as a hen’s egg, and sometimes so small that they can scarcely be perceived by the naked eye.
When the rocks of grey wacka are not covered by those of any other formation, they form round-backed hills, usually insulated towards the tops, and intersected by deep valleys. They are widely distributed: and are often extremely rich in ores, both in beds and veins. Almost all the mines of copper, lead, and zinc, in the Hartz, are in grey wacka; and, in Transylvania, this species of rock is traversed by numerous small veins of gold.
2. FLOETZ, OR FLAT ROCKS.
267. OLD RED SANDSTONE, or MILLSTONE GRIT, is a floetz or flat rock, composed of large grains of sand or quartz ([76]), coloured by oxide ([21]) of iron, and usually cemented together by a kind of clay.
In several parts of Derbyshire this kind of rock forms the uppermost stratum; and in some places, is known to be 120 yards thick.
What are known by the name of peak millstones are formed of millstone grit. They are chiefly obtained from quarries near Nether Padley, in Hathersede, Derbyshire; a very inaccessible part of the country, but where the stone is of better quality than it can elsewhere be procured. These millstones are made of different dimensions, from two feet in diameter, and eight inches thick, to five feet and half in diameter, and seventeen inches thick.
Some of the beds of millstone grit, which have spherical stains in them, of light red colour, are said to be infusible; and are consequently a valuable stone for lining the hearths of iron and other furnaces, where an intense heat is required. These are called firestones, and Roches quarry, near Upper Town, in Ashover, Derbyshire, is famous for them.
The upper beds of this kind of rock are often thin, and capable of division, so as to make excellent paving stones, or flags. There is a particular bed of it at Stanton, in the Peak of Derbyshire, so porous that it is made into filtering stones for the cleansing of turbid water.
268. THIRD SANDSTONE, GRITSTONE, or FREESTONE, is another kind of floetz or flat rock, formed of very small agglutinated particles of sand. It is opaque, usually of whitish colour, and found in large masses, of various degrees of hardness.
The name of freestone has been given to this kind of rock, from its capability of being broken or hewn, with nearly equal facility, in any direction. Hence, as well as from its great durability, it is peculiarly esteemed for buildings. It is also formed into cisterns and troughs of various kinds; into pillars for supporting corn ricks; into rolling stones; and into grinding stones for cutlers, edge-tool makers, and workers in polished steel. Paviors’ flags, or the stones used for the paving of footpaths, yards, kitchens, and out-houses, are generally flat pieces of freestone.
Scythestones, or stones for the sharpening of scythes upon, are made of freestone. Considerable numbers of these are wrought in Derbyshire; and the dexterity that is displayed in cleaving and forming them is somewhat remarkable. The workmen use sharp-pointed picks, several very small wedges, and a hammer. A proper block of stone being selected, two or three of these small wedges are set in a row, by gentle blows of the hammer. These blows are successively repeated till the stone splits. The wedges are then set in a straight line into the face of the piece split off, and the stone is cleft again in that direction. In this manner the sub-divisions are continued, until a piece remains of size to make two scythestones, each an inch and a half square, and about twelve inches long. This the workman holds in his left hand, nearly upright; with the point of his pick he traces a deep nick down the middle of first one side and then the other; and then by a slight blow of his pick he separates it, into two, so dexterously, that not more than three or four in a hundred are broken in the cleaving. Such stones as are intended for round rubbers, are first reduced into an octagonal shape by the point of the pick, and then handed over to women and boys, who grind or rub them in a notch formed in a hard stone, until they are of the requisite shape. The square ones are finished by being ground on a flat stone.
Other rocks, belonging to what is called the floetz, or flat formation, have been already mentioned, under the heads of lime-stone ([140]), gypsum ([192]), rock salt ([202]), chalk ([141]), and coal ([217]).
III. ALLUVIAL DEPOSITIONS.
269. These are described to comprehend all such substances as have been formed from previously existing rocks, of which the materials have been worn down, by long exposure to the agency of water and air, and afterwards deposited in nearly horizontal beds on the surface of the land. Alluvial deposits have been formed, and are still forming in every quarter of the globe. They occur both in mountainous regions and in flat countries, filling up the valleys or hollows in the one; and often forming vast and extended plains in the other.
They consist of peat, sand, gravel, loam, clay, and other substances.
IV. VOLCANIC ROCKS.
270. Volcanic rocks are composed of such mineral substances as have been ejected from volcanoes, or have been formed by the agency of subterraneous fires, and have undergone certain changes in such fires.
They are of two kinds; the one called pseudo volcanic, such as burnt clay, porcelain jasper, and earth-slag, which have been altered in consequence of the burning of beds of coal in their neighbourhood; and the other, called true volcanic minerals, such as stones, ashes, and lava, which have been thrown out of real volcanoes.
271. It will somewhat tend to illustrate the history of the mineral kingdom, to state, in conclusion, under a tabular form, the relative heights of the principal mountains, or masses of rocks, which occur in the different countries of the world; previously remarking, that the most lofty and magnificent of these, respecting which any account sufficiently authentic has hitherto been obtained, are the mountains of Nepaul and Thibet, in Asia, one of the former being 27,667, and the highest of the latter measuring at least 23,262 feet, or from 4½ miles to 5¼ miles in perpendicular height above the level of the sea. Previously to the knowledge that has lately been attained respecting the Asiatic mountains, those of the Andes, on the continent of South America, had been considered by far the highest in the world. One of them, Chimborazo, is 20,900 feet in height. Of the European mountains, the highest is Mont Blanc, in Switzerland, which measures 15,680 feet, or about 2¾ miles. The loftiest summit within the British islands is Ben Nevis, in Inverness-shire, Scotland, which does not exceed 4,380 feet, or somewhat more than three quarters of a mile; and the great pyramid of Egypt, the loftiest work of human art and industry with which we are acquainted, and which will serve as a point in the scale, measures only 477 feet.
272. It has been remarked that the greatest altitude at which bananas and other palm-trees grow in America is about 3280 feet above the level of the sea ([Frontispiece, Fig. 48]): that in the torrid zone, the superior limits of oaks is about 10,500 feet ([49]), of pines 12,000 feet ([50]), and of lichen plants 18,225 feet ([51]). The American travellers, Messrs. Humboldt and Bonpland, on the twenty-third of June, 1802, ascended the mountain of Chimborazo to the height of 19,400 feet ([52]). The highest flight that has been remarked of the South American vulture, called the condor, was 21,000 feet ([53]). M. Lussac, on the 16th of September, 1804, ascended in a balloon from Paris, to the height of 22,900 feet. In Switzerland, the limit of perpetual snow is above the altitude of 9000 feet ([54]).
Height of the Principle Mountains.
British Islands.
| Scotland | Ben Nevis, Inverness-shire | 1 | 4380 |
| Ben Lawers, Perthshire | 2 | 4051 | |
| England | Skiddaw, Cumberland | 3 | 3530 |
| Cross Fell, Cumberland | 4 | 3390 | |
| Helvellyn, Cumberland | 5 | 3324 | |
| Wharnside, Yorkshire | 6 | 2480 | |
| Ingleborough, Yorkshire | 7 | 2380 | |
| Wales | Snowdon, Caernarvonshire | 8 | 3568 |
| Cader Idris, Merionethshire | 9 | 3550 | |
| Ireland | Macgillicuddy’s Reeks, Kerry | 10 | 3404 |
| Sleibh-Dorin, Londonderry | 11 | 3150 |
Continent of Europe.
| France | Mont d’Or, Auvergne | 12 | 6707 |
| Puy de Sausi, Auvergne | 13 | 6700 | |
| Pyrenees | Mont Perdu, the highest of the Pyrenees | 14 | 11,283 |
| Le Pic Blanc, Spain | 15 | 10,205 | |
| Alps | Loucira | 16 | 14,451 |
| Loupilon | 17 | 14,144 | |
| Switzerland | Mont Blanc, highest mountain in Europe | 18 | 15,680 |
| Mont Rosa | 19 | 15,555 | |
| Mont St. Gothard | 20 | 10,014 | |
| Italy | Mont Cimone | 21 | 6401 |
| Vesuvius | 22 | 3900 | |
| Germany | Ortler-Spitze, Tyrol | 23 | 15,430 |
| Ostelle, Saltzburg | 24 | 12,800 | |
| Carpathian Mountains, highest summit | 25 | 8640 | |
| Lomnitz Peak | 26 | 8640 | |
| Sweden | Areskutan, Jempland | 27 | 6180 |
Islands.
| Teneriffe | Peak of Teneriffe | 28 | 12,236 |
| Sicily | Ætna | 29 | 10,963 |
| Jamaica | Blue Mountains | 30 | 7431 |
| Iceland | Snæfiel | 31 | 6860 |
| Hecla | 32 | 4900 |
Asia.
| India | Dhawalgeri in Nepaul | 46 | 27,667 |
| Mountains of Thibet | 47 | 23,262 | |
| Turkey | Mount Lebanon, estimated at | 33 | 9520 |
| in Asia | Mount Ararat, estimated at | 34 | 9500 |
| Mount Ida | 35 | 4960 |
America.
| Andes, South | Chimborazo, Quito | 36 | 20,900 |
| America. | Cotopaxi, Quito | 37 | 18,880 |
Height of Remarkable Lakes, Cities, &c.
| Alps | Lake of Lausanne | 38 | 8640 |
| Lake of Lanzon, on the mountain of Olan | 39 | 6797 | |
| Switzerland | Lake of Lucerne | 40 | 1408 |
| South America | City of Riobamba, Quito | 41 | 18,800 |
| City of Quito | 42 | 9356 | |
| North America | City of Mexico | 43 | 7424 |
| Austria | Town of Eisenerz | 44 | 2056 |
| Egypt | The great Pyramid | 45 | 477 |