Rock carving

“ In order to make the age of the North American rough-stone implements clear, we must study the geological evidence.
Clay and gravel are made, we know, from the primitive rocks. The atmosphere and the rain loosen large pieces of rock from the mountains, and they are broken in the beds of streams by the action of the water. The fine particles are produced by the rubbing of the stones together; the water grinds the broken rocks down smooth, and makes pebbles of them. Gravel, sand, and clay, produced in this manner, become sorted out by the action of the water, or stratified. ”

“ Disintegration has penetrated the rock far below the surface and the large crystals are held together with but little more tenacity than prevails in a bed of gravel. Moisture and even roots penetrate it deeply and readily and the crystals fall apart with thrusts of the knife blade, the rock crumbling with the greatest freedom. ”

“ Is it the story of all jasper (quarries in the United States? Is it the story as well of the argillite sandstone and quartzite quarry sites and the obsidian workings not yet discovered and studied? In a word, are we right in supposing that this process of passing from the shapeless block (Fig. 7) to the "turtleback," and from the "turtleback" to the thin, leaf-shaped blank, and thence to the spear or finished implement, represents the necessary steps through which all peoples in an age of stone have passed in the fashioning of their rock-hewn tools? ”

“ The central cores of many of the now deeply eroded ranges consist of granite and other similar rocks, and are surrounded by sedimentary beds which range in age from the oldest stratified rocks now known to the youngest. Igneous rocks in great variety and in all forms incident to an extruded or volcanic and intruded or plutonic origin are present. The many disturbances that have occurred have led to the formation of mineral veins and the impregnation of rock masses with ores of various kinds—such as gold, silver, lead, copper, etc.—which have been mined with great success at many localities. ”

“ It is true that there seems to have been at one time an itch for carving, for in certain regions every piece of stone that projected from the ground has been carved as it lay, without any attempt to remove it: perhaps, a beneficent influence was created with each serene carved face. ”

“ As you52 look down over the dark crags of millstone grit, great, grey, pavement-like masses of limestone strike the eye, standing above the heather, perfectly bare, and in the distance resembling clearings, and in rainy weather sheets of snow. On approaching them the surface of erosion becomes more and more apparent, and the shapes due to the mere accident of varying hardness in the rock, or the varying quantity of water passing over it, present a most astonishing variety. ”

“ Geologically considered, the results which they accomplish, may be summed up under the two heads of deposition and erosion—the formation of new rocks in the sea, and the destruction of old rocks on the land. In the rôle of rock-makers they produce the very important original structures of the stratified rocks; while as agents of erosion they develop the most salient of the subsequent structures of the earth’s crust—the infinitely varied relief of its surface. ”

“ In the side of a stony hill on which scarcely a plant grows, a narrow passage, a few feet wide, has been quarried, and air shafts have been cut down into it through the solid rock with prodigious labour. I followed this passage until a falling in of the roof prevented me from going any farther. I could perceive no trace of a metallic vein, so thoroughly had it been worked out, but scattered over the hillside with schist, talcose slate, and fragments of quartz, was a great deal of scoriae, showing that metal of some kind had been excavated, and that the smelting had been done on the spot. ”

“ Rocks are softened by being wet. Streaks of iron in the hardest granite will rust out and let the water in. Then the lime in rocks is easily dissolved. Every dead leaf the river carried along added an acid to the water, and this made easier the process of dissolving the limestone.
Every crumbling rock gives the river tools that it uses like hammer and chisel and sandpaper to smooth all the uneven surfaces in its bed, to move stumbling blocks, and to dig the bed deeper and wider. The steeper the slope is, the faster the stream flows, and the larger the rocks it can carry. ”

“ No sooner are residual weathered mantles formed or sedimentary rocks deposited, whether under air or water, than processes of consolidation begin. Settling, infiltration of cementing materials, and new growths, or recrystallization, of the original minerals of the rock all play a part in the process. The mud or clay becomes a shale, the sand becomes sandstone or quartzite, the marl becomes limestone or marble. ”

“ One of the modes in which large blocks of granite may be severed from [Pg 124] a rock, is exemplified by what takes place in some parts of India at the present day. The quarryman, having found a portion of the rock sufficiently extensive, and situated near the edge of the part already quarried, lays bare the upper surface, and marks on it a line in the direction of the intended separation, along which a groove is cut with a chisel about a couple of inches in depth. Above this groove a narrow line of fire is kindled, and maintained till the rock below is thoroughly heated ”

“ In some places, this clay drift yields balls of iron pyrites, which renders the water unpalatable. At what depth the rock would be struck, if the excavation were continued, can only be conjectured. A well has been dug, a short distance below the city, upwards of sixty feet, chiefly through clay and gravel, without reaching the rock; but abraded fragments of granite and hornblende rocks were thrown from the greatest depths. ”

“ It is applicable to every form of rockwork, such as tunnelling, mining, quarrying, open cutting, shaft-sinking, or submarine drilling; and in hard rock, like granite, gneiss, ironstone, or quartz, the machine will, according to size, progress at the incredible rate of four inches to twelve inches per minute, and bore holes from 3⁄4 in. up to 5 in. diameter. It will, on an average, go through 120 ft. of rock per day, making forty holes, each from 2 ft. to 3 ft. deep, and it can be used at any angle and in any direction, and will drill and clear itself to any depth up to 20 ft. ”

“ Rock taken from the surface, which has been exposed to the atmosphere, is of an inferior quality to that found at a depth where it has been exposed to a strong pressure; and is consequently denser. Therefore, in opening a quarry it is advisable to excavate upon a hill-side and come at once to the sound stone. Rock is generally found in beds, divided by joints or seams, at which the natural adhesion is broken and the layers are easily separated. ”

“ The method just outlined is called the center-heading method, and was the most satisfactory plan devised for full-rock sections.
Excavation in Part Rock and Part Earth.—This was probably the most difficult work encountered, particularly when the rock was covered with boulders and coarse sharp sand which permitted a free escape of air. It was necessary, before removing the rock immediately under the soft ground, to excavate the earth in advance of the shield to a point beyond where the rock was to be disturbed, and to support, in some way, the roof, sides, and face of the opening thus made. ”

“ The greatest proportion of the rocks are in that state which the quarries term rotten; which means, that when a block of the stone is struck with the hammer, it breaks into a number of small irregular fragments, frequently not exceeding the size of a walnut, the surfaces of which are generally covered with oxide of iron, probably arising from a partial decomposition. This is the case, not merely near the surface, but in some degree even where the rock has been quarried to a considerable depth. ”

“ Cave students are often confused by another deposition found in the form of thin blades jutting out of the wall (see illustration below) . They have a woven, crystalline texture. Prior to removal by solution, some of the marble cracks were filled with calcium carbonate. Being less soluble than marble, the sheets of calcite crystals remain for a time after the surrounding rock is dissolved away.
Blade formation
So far we have discussed cave features—speleothems—created by deposition of mineral from the solid to liquid, and back to solid state. ”

“ Rocking-stones.—Just on the borderland between the works of Nature and Art comes the so-called Rocking-stone, or Logan-stone, which is usually nothing more than an ice-transported boulder, poised so nicely on its rocky bed that gentle pressure by the hand may cause it to rock, or oscillate. ”

“ I may further urge that, had the object of the workman been solely to deceive, he would have scarcely selected a stone whereon to carve of a granite character, and especially a piece of granulite, one of the hardest of rocks to work, being not only hard in quality but of crystalline structure, and ill-adapted for receiving a polish, at least under rough tools. Granting, however, that for the reason stated we are justified in assigning the origin of the carving to the Indian period, there still remain many difficulties in the way of determining its object or meaning. ”

“ When gravel is rolled along in the channel of a stream there is friction between it and the bed over which it moves. If the pebbles be as hard as the bed over which they are rolled their movement must result in its wear, and even if they be softer more or less wear takes place. As the moving stones wear the121 rock of the stream’s bed they are themselves worn by impact with it and with one another. In all cases the softer material suffers the more rapid wear. The first effect of wear on materials in transportation is the reduction of their rugosities of surface. ”

“ Most of the limestone rock disclosed by excavation in the mines, is of the granulated kind; while the structure of the rock above the surface, where the strata are exposed to the weather, as in cliffs and hill-sides, is of the solid, glistening, pseudo-compact variety. ”

“ Occasionally, however, the workmen seem to have gathered rounded stones of other varieties of rock, though nothing equaling the firmness of the above, and so fit for the purpose of a rude hammer in simple mining, can be selected among all the rocks of the region. ”

“ The conditions under which the instrument is worked are obviously such that this edge will be rapidly worn down by attrition from the hard rock material, and by fracture. To withstand these destructive actions, two qualities are requisite in the material of which the instrument is composed, namely, hardness and toughness. Thus there are three important conditions concurring to determine the nature and the form of a cutting tool to be used in rock boring—1, a necessity for a cutting edge ”

“ The softer species of rock may be scratched with the nail. It has an uneven fracture, inclining to earthy. This rock abounds with iron, insomuch that the magnet is enabled to attract very small particles of it. It resists a very strong flame of the blowpipe without being fused. The line edges however of the harder species seem to yield a little to its action.
In the side of the hill, below the ridge of rock, a quarry is opened for the purpose of supplying the neighbouring road with stones. Here the rock is laid bare in large masses. ”

“ Many varieties of rocks are to be found among the gravel pebbles, but the rocks of igneous origin and possessing a considerable degree of hardness generally predominate. Intermixed with the pieces of rock there is likely to be clay or other soil, the quantity varying greatly in different deposits and even in various places in the same deposits. ”

“ The absence of soil and the smoothness of weathered surfaces render quartzite mountains hard to climb. The uniform cementing of the rock leaves the bedding with little influence on the surface-features, and rock-ledges and shelves are rare. The traveller ascends over taluses of angular and obstinate blocks towards slippery and inhospitable domes. But the wildness of the scenery will be his sure reward. ”

“ Scrambling in home quarries, on chalk, gravel, blue-stone,—all kinds of rock,—is excellent practice. The surfaces are, however, raw and untempered by time, and the crude fractures and ledges by which we climb are made by man and survive by no natural law of the fittest. No experience of rock structure can therefore suffice to allow of calculation upon their security. Each hold must be separately tested before use. The risk is generally out of all proportion to the height. A rope from above should be used on any passage of doubt. ”

“ In all countries the fundamental rock on which the boulder formation reposes, if it consists of granite, gneiss, marble, or other hard stone capable of permanently retaining any superficial markings which may have been imprinted upon it, is smoothed or polished, and exhibits parallel striae and furrows having a determinate direction. ”

“ The fissures which contain the ore are proved very frequently, by their scratched and grooved sides, and polished surfaces or slicken-sides, to have been the result of subterranean movements by which the rock has been broken by mechanical force. ”

“ The crust of the lithosphere.—Much of the detritus washed down from the land finds its way to bodies of standing water, and beneath lakes and seas the mantle of loose material is made up largely of the gravel, sand, and mud derived from the land. Before deposition these materials are more or less assorted and arranged in layers by waves and currents. When consolidated they constitute rock. The weathering of the rocks of the land, the wearing away of the resulting detritus, and its deposition beneath standing water, are among the most important processes of geologic change. ”