Stone (geology)

“ On the lower slopes, even under the tapestry of verdure which nature delights to hang where she can over her naked rocks, we may detect the same pervading influence of the joints upon the forms assumed by ravines and crags. Each kind of stone, too, gives rise to its own characteristic form of scenery. Massive crystalline rocks, such as granite, break up along their joints and often decay into sand or earth along their exposed surfaces, giving rise to rugged crags with long talus slopes at their base. ”

“ It is a softer stone than marble, and more easily wrought.
Forms of stratification.—A series of strata sometimes consists of one of the above rocks, sometimes of two or more in alternating beds. Thus, in the coal districts of England, for example, we often pass through several beds of sandstone, some of finer, others of coarser grain, some white, others of a dark colour, and below these, layers of shale and sandstone or beds of shale, divisible into leaf-like laminæ, [p.14] and containing beautiful impressions of plants. ”

“ The crystalline arrangement of the lime in the organic structures enables them to resist disintegration better than the general mechanically aggregated matrix of the rock. An experienced fossil collector will always search well such weathered surfaces, for he often finds there, delicately picked out by the weather, minute and frail fossils which are wholly invisible on a freshly broken surface of the stone. Many rocks weather with a thick crust, or even decay inwards for many feet or yards. ”

“ Rocks are poor conductors of heat, and hence their surfaces may become painfully hot under the full blaze of the sun, while the interior remains comparatively cool. By day the surface shell expands and tends to break loose from the mass of the stone. In cooling in the evening the surface shell suddenly contracts on the unyielding interior and in time is forced off in scales.
Many rocks, such as granite, are made up of grains of various minerals which differ in color and in their capacity to absorb heat, and which therefore contract and expand in different ratios. ”

“ Stony Rises.--The stony ground, in contradistinction to the sandstone ranges, appears to have been formed from the detritus of the latter, deposited in undulating beds of vast extent. The greater portion of this ground appears almost level when one is on it, but when viewed from a distance the undulations are very distinct; the stones are chiefly water-worn pebbles of sandstone, quartz, and iron-stone; in some places the rises approach more nearly to the nature of the sandstone ranges, and here the stones are less water-worn, and are mixed with large blocks of rock. ”

“ Rounded boulder shaped mountains of granite or igneous rocks are to me far more impressive than much taller ones of other formations. One feels that they are solid, and are welded to the central foundations of earth; that they were the offsprings of primal overpowering heat, while the others are made up of tiny particles of disintegrated igneous stone, loosely thrown together by glacial moraines or dropped at ocean's bottom, and after eons of time compressed into hardness. ”

“ All these modern stones appear to be hard and solid when they are first hewn out, but when, exposed to the weather, the air and rain presently dissolve them; their substance is so different from true stone, that when reduced into minute parts, to make sand of them, they are converted into a kind of earth or clay. ”

“ Other stones, such as ‘fired’ zircon, white sapphire, white topaz, and rock-crystal, may dazzle with brilliancy of light reflected from the surface or emitted from the interior, but none of them, like diamond, glow with mysterious gleams. No hint of colour, save perhaps a trace of the blue of steel, can be tolerated in stones of this category; above all is a touch of the jaundice hue of yellow abhorred. It taxes all the skill of the lapidary to assure that the disposition of the facets be such as to reveal the full splendour of the stone. ”

“ When discussing the ages of the Plutonic rocks, we have seen that examples occur of various primary, secondary, and tertiary deposits converted into metamorphic strata near their contact with granite. There can be no doubt in these cases that strata once composed of mud, sand, and gravel, or of clay, marl, and shelly limestone, have for the distance of several yards, and in some instances several hundred feet, been turned into gneiss, mica-schist, hornblende-schist, chlorite-schist, quartz rock, statuary marble, and the rest. ”

“ In districts where stone is more inaccessible it is constructed of stones mixed with earth and clay, and at some few points it is entirely of earth. It has been strengthened at intervals with fortified stations, like the Roman walls from which its model is supposed to be derived. ”

“ METEORIC STONES are a species of iron ore, which have at different times been known to fall from the atmosphere.
194They have been seen only in shapeless masses, of from a few ounces to several hundred pounds in weight. Their texture is granular. They are covered externally with a thin blackish crust, and are, internally, of an ashy grey colour, mixed with shining minute particles.
There is sufficient evidence to show that solid masses of stone have been observed to fall from the air at a period considerably anterior to the Christian era. ”

“ After a little they turned off toward a tremendous rock of solid granite that had been cleft smoothly in twain by some gigantic force of nature, and, walking between the towering walls of stone, came out on the farther side upon a small level space, where immense ferns and flags grew thickly in the rich soil, held in place and kept damp by the great cool masses of stone. ”

“ In our own country, and in many other parts of the world, we find fragments of stone distributed over the surface, sometimes in the form of enormous blocks, bearing in their fresh angles evidence that they have been little disturbed since their disruption, but sometimes much rubbed and worn, and broken into smaller pieces, till they form what is known as gravel. ”

“ The rock which stands in competition with granite for the title of primitive in the order of mountains, is that micaceous stratified stone which is formed chiefly of quartz, but which admits of great variety like the granite. The difference between those two bodies does not consist in the materials of which they are composed, for, in their varieties, they may be in this respect the same, but in a certain regularity of composition, in this alpine stone, which evidently arises from stratification or subsidence in water. ”

“ They are always perpendicular in the strata of calcinable matters, as chalk, marle, marble, &c. but are more oblique and irregularly placed in vitrifiable substances, brown freestone, and rocks of flint, where they are frequently adorned with [49] chrystals, and other minerals. In quarries of marble or calcinable stone, the divisions are filled with spar, gypsum, gravel, and an earthy sand, which contains a great quantity of chalk. ”

“ It is to similar accidents we must attribute the origin of all the large stones found adjacent to the mountains. We must recollect, as before observed, that these large stones, scattered abroad, are more common in countries whose mountains are composed of sand and free-stone, than in those where their composition is marble and clay, because sand is a less solid foundation than clay. ”

“ The stone is chiefly granite, the rugged rocks of which lie like knobs of sugar over the surface of the little hills, intermingled with sandstone in a highly ferruginous state; whilst the soil is an accumulation of sand the same colour as the stone, a light brownish grey, and appears as if it were formed of disintegrated particles of the rocks worn off by time and weathering. Small trees and brushwood cover all the outcropping hills ”

“ A close-grained stone called lithographic stone (a kind of magnesian limestone) is ground perfectly even on the surface, and (if for being written upon) polished with pumice-stone, or (if for being drawn upon with chalk) grained with fine sand; the design is drawn with chalk or ink, each of which is made up of greasy materials—wax, soap, and asphaltum, colored with lamp-black. When the design is made, the stone is etched—washed over with a weak mixture of nitric acid and water—which answers three purposes ”

“ Limestone, sandstone, and clay, which constitute so many of the stratified masses, are forms of mineral aggregations such as never occur among granites, basalts, porphyries, &c., which make up a large portion of the unstratified rocks. ”

“ The stone is faced with a precision that no skill can excel, its right angles turned with an accuracy that the most careful geometer could not surpass. I do not believe there exists a better piece of stone-cutting, the material considered, on this or the other continent. ”

“ For, whereas, in the first forty years of the present century, the dead languages, especially Latin and Greek, history, logic, and metaphysics, fairly held their own against the computative sciences of mathematics, mechanics, physics, and chemistry, and the systematic or classificatory subjects of botany, geology, and zoology as topics of teaching and examination, they seem at the end of the second forty to have been all but superseded. No doubt in the main the revolution, great as it undoubtedly is, has proved salutary. ”

“ Thus mountains, whereon we see points or peaks, are generally vitrifiable rock, and those whose summits are flat, mostly contain marble and hard stones filled with marine productions. It is the same with respect to hills, for those containing granite, or free-stone, are mostly intersected with points, eminences, cavities, depths, and small intermediate valleys; on [288] the contrary, those which are composed of calcinable stone are nearly equal in height, and are only interrupted by greater and more regular vallies, whose angles are correspondent ”

“ It is applied to every large mass of mineral matter that goes to form the Crust of the Earth, whether it be hard and strong, or soft and plastic. Thus, for example, gravel and clay, coal and slate, are called Rocks, just as well as limestone and granite. ”

“ Long experience in archæological field-work has fully convinced me that, in the vast majority of instances, stone implements are practically in the same position that they were when buried, lost, or discarded. A single specimen or many of them might mislead; but it becomes safe to base a conclusion upon the locality, when we have the material in such abundance as in this instance of these rude spear-points, and find that fully eighty per cent are from the alluvial mud of the river meadows, or such isolated upland areas as have been described. ”

“ The same causes that produced the layers of peat or sand, or limestone, or clay, which we find by examination of the earth's surface, are acting to-day. Coal is forming now; and so is limestone; and so is sandstone; so even is granite. But these layers or strata form very slowly, so that since man has kept historical records the thickness of new strata laid down could be measured in inches. ”

“ And, as I shall add my own conclusions without reserve; because the whole of the phænomenon tends greatly to confirm some ideas which I had previously been led to form, many years ago, concerning the consolidation of certain species of stone; it may open a door for further curious investigation.
And it may at least amuse, if not instruct; whilst I add a short detail of uncommon facts, recorded in antient history, and tending to shew clearly, that we are not without precedents of similar events having happened, in the early ages of antiquity. ”

“ The largest stone, which weighed 103 pounds, struck the earth at the foot of a large oak-tree, and, after cutting off two roots, one five inches in diameter, and grazing a third root, it descended two feet ten inches into hard clay. ”

“ Rocks.—Every one knows that the crust of the earth is composed of very various substances, some of which are hard and crystalline in texture, like granite; others less indurated and non-crystalline, such as sandstone, chalk, shale, &c.; while yet others are more or less soft and incoherent masses, as gravel, sand, clay, peat, &c. ”

“ But when we examine these aged stones we find that they themselves appear as the cemented residues and stratified deposits formed from some yet preëxistent firmament of land. In serial bands, conforming to each other, as book lies against book, we find limestone, slates, sandstones, quartzites, schists, and gneiss, and we know now that these regular layers, hard, distinct, and characterized by color, constituents, and adventitious minerals, were once water-drifted beds metamorphosed, transfigured, as it were, by heat and pressure into this adamantine pavement ”

“ Viewing the whole of this compound mass of schist and limestone as a single rock, and the granite as another, it is easily seen on the most superficial glance, from the strong contrast between the dark grey of the former and the red of the latter, that the dark rock is intersected and disturbed by innumerable veins of granite. These traverse it in every possible direction, and are of various sizes, the smallest not exceeding that of a thread, and reticulating the dark rock in a most intricate and amusing manner. ”

“ Heavy stones.
The largest stones cannot usefully have any case; as a case which would not be cracked up by the weight in moving, would be so thick and heavy that it would make the stone far less moveable. ”

“ If we descend into the Crust of the Earth we may trace this building even from the foundations, which are laid upon the solid granite, up through each successive stage of limestone, and sandstone, slate, conglomerate, and clay, until we come to the surface, where new strata, composed of the same elements, and exhibiting the same general characteristics, are slowly growing up before our eyes. ”