Borehole

“ In sand below water there are, of course, no open fissures, and even if adits could be Wells in sand. usefully employed, the cost of constructing and lining them through the loose sand would be prohibitive. The well itself must be lined; and its yield is therefore confined to such water as can be drawn through the sides or the bottom of the lining without setting up a sufficient velocity to cause any sand to flow with the water. Hence it arises that, in sand formations, only shallow wells or small boreholes are commonly found. ”

“ When pits cannot be sunk, it is desirable that in a suspectedly treacherous site the bore-holes should be at every 200 or 300 feet.
Excavating pits, using test-bars, and driving piles are some of the methods of determining the character of foundations, but care should be taken to ascertain in boring that boulders, or thin strata of hard gravel, are not mistaken for solid rock. In sand, mud, or soft clay they can be made by means of an iron pipe and the water-jet system. Experience has proved that boring with an auger is not so reliable as boring with a tube, such as is used for artesian wells. ”

“ Springs are common in the alluvion, and more frequently than in the case of drift, they can be found by boring. As the surface, which is covered by the deposit, is extensive, the water circulates from a distance through permeable strata often overlaid by others that are impervious. If at a considerable distance from the points of infiltration, and at a lower level, a boring be put down, the water will ascend in the bore-hole in virtue of its tendency to place itself in equilibrium. ”

“ Along the course of the larger streams huge chambers occur; for the ever-eddying water, bearing sand along in its course, eats out the sides of its channel, or, revolving stones in its bed, carves out the pothole by friction. Or some pendent mass of rock has its support undermined and comes crashing into the streamway, only to be broken up and carried away by the ceaseless energy of the stream, so ever enlarging the chambers upwards towards the light of day. But whilst this action is going on underground, a more potent factor is at work where the subterranean stream first sees the light. ”

“ After every shower, the stream comes down red and turbid with the finer and more argillaceous portions of the deposit; minute accumulations of sand are swept to the gorge of the ravine, or cast down in ripple-marked patches in its deeper pools; beds of pebbles and gravel are heaped up in every inflection of its banks; and boulders are laid bare along its sides. Now, a separation, by a sort of washing process of an analogous character, must have taken place in the materials of the more exposed portions of the boulder-clay, during the gradual emergence of the land ”

“ A running sand in soft clay is, however, the most serious difficulty met with in well boring. Under such circumstances the bore-hole has to be tubed from top to bottom, which greatly increases the expense of the undertaking, not only by the cost of the tubes, but also by the time and labour expended in inserting them. When a permanent water supply is the main object of the boring, the additional expense of tubing the bore-hole is not of much consequence, as the tubed hole is more durable, and the surface water is thereby excluded ”

“ The scratches on the rock floor are parallel grooves, all of which trend southward. They are unmistakable tracks left by glaciers, and the boulders are like the stones perched on glacial ice for a ride to the terminal moraine.
The land above the old lake shore is bare scratched rock or rocky soil called boulder till. Every hill farm has been cleared of more stones than trees, and it is only with the vogue of the rock garden that these erratics have found any merit in man’s estimation. ”

“ What had once been a waterhole was a red and yellow heap of shale, fragments of stones, gravel, and sand. There was no water, and the sheep were bleating. August dismounted and climbed high above the hole to examine the slope; soon he strode down with giant steps, his huge fists clinched, shaking his gray mane like a lion.
“I've found the tracks! Somebody climbed up and rolled the stones, started the cave-in. Who?”
“Holderness's men. They did the same for Martin Cole's waterhole at Rocky Point. How old are the tracks?”
“Two days, perhaps. We can't follow them. What can be done?” ”

“ Incidentally, bore-holes supply information as to the character and depth of the valueless depositions of earth or rock overlying the mineral deposit. Such data assist in deciding upon the appropriate method for, and in estimating the cost of, sinking shafts or driving tunnels for the development and exploitation of the deposit. In sinking petroleum wells, boring serves not only for discovering the oil-bearing strata but also for extracting the oil. This industry has become of great importance in many parts of the United States, in southern Russia and elsewhere. ”

“ A few rods farther up the stream, the land grew steeper and the walls of the ravine drew more closely together. Taller trees presided over the torrent, and the water struggled downward between larger boulders. A stream, tumbling 22 down its narrow bed, came from the high eastern ledges and met that which poured from the heights on the west. Here, in the perpetual music of falling drops, where one or another of the great walls of the gorge always casts a deep shadow upon the ferns, is the heart of the mountain, the birthplace of the twilight. ”

“ The Dudlow Lane well is also oval, 12 feet by 9 feet, and is sunk to a depth of 247 feet from the surface of the ground. Headings have been driven from the bottom of the well for a total distance of 213 feet, and an 18-inch bore-hole has been sunk to a depth of 196 feet from the bottom of the well, which is chiefly in a close hard rock, with occasional white beds from which the water is mainly obtained. The yield is nearly 1,500,000 gallons a day. ”

“ Near the waterfall is a cave, where the soil is either sunk, or washed away by the water; it is a narrow deep crack in the earth, which you cannot behold without shuddering. When the water is high, there are three falls. The middle one precipitates directly down, the two others cross over the middle one. The drought, however, of the summer of 1825, and a canal, which drains the water from the river to drive saw and other mills, has lessened the quantity of water in the river, so that only one of the three falls has water, and instead of seeing the other two, you perceive the bare rock. ”

“ The sand-ridge ran back from the water-hole a good way (there was a big kurrajong-tree beside it, I remember) , and spread out near upon a mile till you got into a fair-sized plain. The ridge—that's the way of 'em in dry country—was covered as thick as they could stand with pine-scrub. An old cattle-track ran right through to the plain, where they used to come to water in the old days when Baranco was a cattle-run. I was dozing on my horse, dog-tired and stiff with the cold, when I came to the water-hole at the foot of this sandhill. I always used to pull up there and have a smoke ”

“ The resistance experienced in boring through different strata is various; and some rocks passed through are so hard, that with 12,000 blows a day of a boring tool weighing nearly 10 cwt., with 19 inches height of fall, the bore-hole was advanced only 3 to 4 inches a day. ”

“ The sinking of artesian wells is another application of boring. They are often hundreds, and sometimes thousands, of feet in depth. A well in St Louis, Missouri, has a depth of 3843 ft.
Boring is useful in mines themselves for a variety of purposes, such as exploring the deposit ahead of the workings, searching for neighbouring veins, and sounding the ground on approaching dangerous inundated workings. In the coal regions of Pennsylvania, bore-holes are often sunk for carrying steam pipes and hoisting ropes underground at points remote from a shaft. ”

“ If the geological deposits of the drainage area are highly impervious, the surface flow will receive and transmit the water into the mass only through the cracks and fissures in the rock. Pervious materials, such as sandstones, sands, gravels, and cracked or fissured rocks, induce seepage, retard runoff, and, if such deposits are underlaid with an impervious bed, provide underground storage which impounds water away from the conditions which permit evaporation, and hence tends to increase runoff and equalize flow. ”

“ To merely drive down iron rods feeling for so-called bed rock, or to make only a few bore-holes with an earth auger should in no instance be considered sufficient. Borings may be found necessary at considerable depths below the surface and in certain classes of material, but dug pits or shafts should always be resorted to for moderate depths and whenever practicable. Only by such means may the true character of the strata underlying the surface, and the nature and condition of the bed rock, if it be reached, become known. ”

“ The work of erosion by grinding out a channel, miles wide and thousands of feet deep, and thousands of miles in length, through wide-extended fields of lava rock, with rolling boulders and pebbles from the distant reaches of the water-shed behind the Selkirk, Sawtooth and Blue mountain ranges of mountains, down through Idaho, British Columbia, eastern Washington, and eastern Oregon, carrying a deep cut through the Cascade and Coast Range mountains to the ocean, may have required a hundred thousand years. ”

“ Everywhere in the ridges encircling these depressions the loose materials and large boulders are so accumulated and embedded in clay or sand that their morainic character is unmistakable. Occasionally, where a ledge of the underlying rock crops out, in places where the drift has been removed by denudation, the difference between the moraine and the rock decomposed in place is recognized at once. It is equally easy to distinguish the boulders which here and there have rolled down from the mountain and stopped against the moraine. ”

“ Besides its chemical activity water exerts among subterranean rocks a mechanical influence which leads to important changes in the topography of the surface. In removing the mineral matter, either in solution or as fine sediment, it sometimes loosens the support of overlying masses of rock which may ultimately give way on sloping ground, and rush down the declivities in the form of landslips. These destructive effects are specially frequent on the sides of valleys in mountainous countries and on lines of sea-cliff. ”

“ Of bogs there are two sorts, the great parental peat deposits that cover the highland, where not too steep for them to lie, and the swamps in the bottoms formed by the oozings from the hills that have been arrested from instant discharge into the rivers by the growth of moss and water-weeds, or are checked by belts of gravel and boulder. To see the former, a visit should be made to Cranmere Pool, or to Cut Hill, or Fox Tor Mire. ”

“ When large areas are undermined, as in submarine coal mining, it is best to have several hundred feet of protecting rock. In Great Britain the law requires that the workings shall be protected by 120 ft. of solid strata. When the presence of underground bodies of Water is known or suspected, advance bore-holes should radiate from the end of the advancing working place so as to give warning of the position of the body of water, these holes being of such length as to ensure a safe thickness of solid rock. ”

“ When the stream is in flood and comes roaring down the rocky gorge bearing along with it a vast amount of mud, gravel, and - 169 - stones, one can easily see how the friction of the transported material must wear down the hard bed and sides of the channel, and how this process repeated month after month and year after year, must aid the decomposing forces in scooping out a deep ravine. From the cascade the ascent of the stream becomes steeper and the run of water is consequently more rapid. ”

“ And as regards the transport of boulders, it fails; the great size and angular form of some—their occurrence at various levels, resting on various strata—sometimes connected with, and sometimes unconnected with sand or gravel—their position frequently on the top of heaps and ridges of gravel, being facts in seeming opposition to such an explanation, even were it conceded that all the depressions now existing on the line of travel, as lakes and seas and valleys, were scooped out subsequently to their transport. ”

“ As a sea cave is drilled back into the rock, it may encounter a joint or crevice opened to the surface by percolating water. The shock of the waves soon enlarges this to a blowhole, which one may find on the breezy upland, perhaps a hundred yards and more back from the cliff’s edge. In quiet weather the blowhole is a deep well; in storm it plays a fountain as the waves drive through the long tunnel below and spout their spray high in air in successive jets. ”

“ When a mountain uplift crosses the course of a stream, it often happens that the rate of uplift is too rapid to be equaled by the corrasion of the stream, and the uprising rock becomes a dam over which the water still runs, but above which there is accumulated a pond or lake. Whenever this takes place, the pond catches all the débris of the upper 126course of the stream, and the water which overflows at the outlet having been relieved of its load is almost powerless for corrasion, and cannot continue its contest with the uplift unless the pond is silted up with detritus. ”

“ From each mountain gorge the products of its erosion are discharged into the valley. The stream which bears the débris builds up the bed of its channel until it is higher than the adjacent land and then abandons it, and by the repetition of this process accumulates a conical hill of detritus which slopes equally in all directions from the mouth of the mountain gorge. At one time or another the water runs over every part of the cone and leaves it by every part of its base; and it sometimes happens that the opposite slopes of the cone lead to different drainage systems. ”