Bedrock

“ With jack, butcher, and table knives, the search was made in the crevices, after stripping the soil from the bedrock with pick and shovel. Next, we conceived the idea of washing the sand and fine gravel in tin pans, but these were scarce and hard to get hold of. Alexander Stephens dug out a trough, leaving the bottom round like a log. He would fill that with sand and gravel that we scraped off the bedrock, and would shake it, having arranged it so as to to pour or run water on the gravel; finally he commenced to rock the trough, which led to the idea of a rocker. ”

“ Drainage is through a small aperture in the north wall, whose outlet is not known. Apparently the bedrock lies at a considerable depth; it is not visible at any point in the steep ravine leading from the mouth of the cave to the river. Formerly a large quantity of ashes covered much of the inner slope of the talus, where it is protected from the weather; but most of them have been hauled away to scatter over the fields. They extend to a greater depth than any digging was ever carried. ”

“ Although any one rock fragment might scrape away only 1 millimeter of rock along a single groove, the total effect is great when multiplied by countless thousands of similar fragments rasping a bedrock surface for hundreds or thousands of years. Glacier ice may also break chunks of rock loose as it overrides them and may even plow up sections of softer rocks. ”

“ Dry cave earth extends back for 65 feet, then comes fallen rock for 100 feet or more. A little stream runs close to the north wall. Cave earth is 5 feet deep on the bedrock at the entrance and rises toward the interior. There is much refuse within and also on the slope in front of the entrance. ”

“ The soil in all the region has a depth only of from one to three feet, while underlying the shallow arable deposit is one immense bedrock, varying in thickness, the average being from three to six feet. ”

“ A "rock shelter," or "shelter cave," is a room or recess formed by atmospheric erosion in the face, usually at the base, of a cliff. The depth from front to back, under the projecting or overhanging [17] unremoved bedrock above, is generally much less than the length as measured along the face of the bluff. They are nearly always dry, more or less protected from storms, and when of suitable size and in a favorable location were much used as camping places. They are rather rare in limestone formations but frequent in massive sandstone. ”

“ Those on the end of the ridge are only 14 feet apart, measuring from their adjacent margins, and were about 16 and 20 feet in diameter as built, both being somewhat widened now owing to the stones having been thrown outward from the central parts by hunters. Each was probably 3 feet high.
The smaller, being least defaced and nearly free from timber, was entirely removed, except a small portion along one margin, and the earth beneath it examined down to the bedrock. There was no sign of a wall; but one that would stand could not be made with stones rounded by weathering. ”

“ From crest to trough they must have been from twelve to fifteen feet high, with the water—on account of the steep declivity and the lack of resistance from rocks—running at race-horse speed. We had become so used to expecting big boulders to underlie heavy waves that it was difficult to realize that there was all of a hundred feet of green water between these giant rollers and the great reefs of bedrock which were responsible for them. ”

“ Dust devils played here and there, little whirlwinds that sent spirals of sand spinning. One of these passed across the train in front of Mangas; it raised a fog of choking sand, out of which the young prospector stumbled, coughing and choking.
Presently his steps became faster. The burros, too, recognized the spot and tried to shove past the man. He prodded them in the ribs, hurled himself forward, spent his last reserve of energy in a spurt that took him to the jumble of black lava and granite outcroppings. There, in a little niche, was the water hole, but it was dry. ”

“ We may indeed accept the implements as being truly characteristic fossils of a certain class of deposits. The character of the beds, consisting as they do, of gravel, sand, and fine silt, brick-earth or loess, and their manner of deposition, are also absolutely in accordance with the river-hypothesis.
On the higher levels above but near the valleys, we frequently find these beds at a considerable distance from the existing stream; we find them at all levels on the flanks of the valleys, and occasionally almost at their bottom, or even below it. ”

“ The bed rock here is found to be polished, scratched and grooved just like the bed-rock in New York; and the scratches extend in the direction from which the ice moves. Resting on the rock are boulders and pebbles (Fig. 22) , sometimes on the bare rock, sometimes imbedded in a clay as they are in the drift. As we found when studying the soil in our own region, so here the pebbles are often scratched, and many of them are quite different from the rock on which they rest. ”

“ The depth of overlying peat affords no safe criterion for calculating the age of the cabin or village, for I have shown in the 'Principles of Geology' (ch. xlvi.) , that both in England and Ireland, within historical times, bogs have burst and sent forth great volumes of black mud, which has been known to creep over the country at a slow pace, flowing somewhat at the rate of ordinary lava-currents, and some times overwhelming woods and cottages, and leaving a deposit upon them of bog-earth fifteen feet thick. ”

“ We come last to the Modern or Superficial Formation, of which the best specimen is the great Bedford level, that spreads over the lower lands of Norfolk, Cambridgeshire, and Lincolnshire, consisting of accumulations of silt, drifted matter, and bog-earth, some of which began before the earliest periods of British history. When these accumulations are removed by artificial means, we find below sometimes shells of recent species, and the remains of an old estuary, sometimes sand-banks, gravel beds, stumps of trees, and masses of drifted wood. ”

“ They were mad, those men, doing the work of giants for the reward of the earth-gnomes. On the ledge under the cliff, the ledge which was flooded at high tide, or had been, were great masses of snow-clear ice like crystal, and under the ice lay the shattered and sundered galleon, and chests plain to be seen. Then there was chopping and splitting of ice, and Frontin dried out the wet powder and tampered with it, and made some of it to burn so that the ice was riven asunder. ”

“ When heaps of this gravel have thus announced our approach to a new formation, we arrive at length at the escarpment of the lacustrine beds. At the bottom of the hill which rises before us, we see strata of clay and sand, resting on mica-schist; and above, in the quarries of Belbet, Leybros, and Bruel, a white limestone, in horizontal strata, the surface of which has been hollowed out into irregular furrows, since filled up with broken flint, marl, and dark vegetable mound. ”

“ It forms the mere filling up of a flat-roofed cavern, or rather of two flat-roofed caverns,—for the limestone roof dipped in the centre to the cornstone floor,—which, previous to the times of the boulder-clay, had lain open in what was then, as now, an old-world deposit, charged with long extinct organisms, but which, during the iceberg period, was penetrated and occupied by the clay, as run lime penetrates and occupies the interstices of a dry-stone wall. ”

“ The loose substances which are found above the solid rocks, in the form of gravel, silt, rolled pebbles, &c., should be carefully distinguished from the solid strata upon which they rest. And the more ancient of these water-worn materials, found on the sides or summits of hills, &c., should be distinguished from the recent mud, sand, and gravel, brought down by land-floods or by rivers. The bones and teeth of quadrupeds are not unfrequently found in the more ancient gravel; and the collection of these remains from distant quarters of the globe is an object of the greatest interest to geology. ”

“ This morning he told us, that the debris of the hills which accumulate in alluvial districts usually continue in the loose form of gravel or sand, or mud, or clay, in which they were deposited. “Their visible transformation,” he said, “into stone is of rare occurrence; in some circumstances, however, especially on the sea coast, we may perceive the consolidation of the sand and gravel into thin strata. If a stream, impregnated with oxide of iron, should empty itself on the beach, it acts as a cement, and the process goes on rapidly. ”

“ All is dry at the base of the escarpment, up to the point at which they commence; and then all is equally dry at the point at which they terminate. And of exactly the same extent,—beginning where the bogs begin, and ending where they end,—we may trace an ancient stratum of pure sand,—of considerable thickness, intercalated between the base of the clay and the superior surface of the Old Red Sandstone. It is through this permeable sand that the profoundly seated springs find their way to the surface,—for the clay is impermeable ”

“ Thus, as the current sweeps along in its course, the sediment which it bears away from the land will be in a manner sorted, and three distinct layers of different materials will be deposited in the bed of the ocean;—first, nearest to the shore, a layer of pebbles and coarse gravel, then a layer of sand, and last of all a layer of fine mud or clay. This is the first step in the construction of stratified rock. To complete the work nothing more is necessary than the consolidation of these loose and incoherent materials. ”

“ The formation of every new deposit by the transport of sediment and pebbles necessarily implies that there has been, somewhere else, a grinding down of rock into rounded fragments, sand, or mud, equal in quantity to the new strata. All deposition, therefore, except in the case of a shower of volcanic ashes, and the outflow of lava, and the growth of certain organic formations, is the sign of superficial waste going on contemporaneously, and to an equal amount, elsewhere. The gain at one point is no more than sufficient to balance the loss at some other. ”

“ Just outside the corporate limits of Bedford, to the south, is an opening in the cliff at the head of a deep ravine, more in the nature of a rock house than of a cave. It would make an excellent shelter for a few persons, being accessible, protected from winds, and close to water. While it may have been so used formerly, the deposit of earth and stone on the floor is very scanty and anything beneath could well be quite modern. ”

“ The eruptions turned the streams from their channels, but on the steeper slope of the mountains the rivers went energetically to work making new beds. They cut down through the lava and the buried gravel until they finally reached the solid rock underneath. Into this rock, which we call "bed-rock," they have now worn cañons two thousand feet deep. The beds of gravel that lay under the old streams frequently form the tops of the hills between these deep cañons. ”

“ Many of the miners decline washing the top dirt at all, but try to reach as quickly as possible the bed-rock, where are found the richest deposits of gold. The bed-rock, which in this vicinity is of slate, is said to run through the entire range, lying in distances varying from a few feet to eighty or ninety below the surface of the soil. ”

“ Water saturated with minerals might easily move through many hundreds of feet of marble strata without further enlarging the openings. Instead, it might even deposit some of the dissolved minerals, filling small cracks and veins, possibly even blocking its own passage during dry cycles when phreatic flow is at a low ebb. The “dry” room in the cave is an example of vein filling. Clay, gravel, and other surface sediments can also be washed into the openings, plugging them up and halting further solution for a time. All these factors lead 12 toward a stabilization of the solution process. ”

“ The rocky roof was flat and smooth, its cracks and fissures fringed with meandering lacework of stalactite. In front, the rocky mole that once held up the reservoir was cloven into a series of Limestone seracs, between which the stream found its way down into the remoter cavities. Masses of clay, some 15 feet thick, deposited by the ancient waters, still flanked this rugged portal into the unknown. Bones of sheep, cattle, horses, and lesser mammals lay about in profusion, enough to reconstruct whole skeletons ”

“ Again, after the formation of the beds many changes may occur in them. They may become hardened, pebble-beds being changed into conglomerates, sands into sandstones, muds and clays into mudstones and shales, soft deposits of lime into limestone, and loose volcanic ashes into exceedingly hard rocks. They may also become cracked, and the cracks are often very regular, running in two directions at right angles one to the other. Such cracks are known as joints, and the joints are very important in affecting the physical geography of a district. ”

“ The beds of shale or plate (as it is called) are very numerous, and are found alternating with the rocks of limestone and sandstone. They are seldom so thick as 7 or 8 fathoms; but the plate sill, which is the lowest bed in the section below that of Dufton, measures 10 fathoms. Shale alternating with sandstone in thin layers sometimes forms beds of considerable thickness, (see section of Hely field,) which are called grey beds: when containing laminæ of hardstone and iron pyrites it is called a girdle bed. Iron pyrites is found imbedded in the shales in great abundance, and in various forms ”