Graver

“ The appearance of the rock, crushed by the [Pg 107] moving mass, is especially distinct in limestone rocks, where grooves are seldom nicely cut, but present the appearance of a violent pressure combined with the grooving power, thus giving to the groove a character which is quite peculiar, and which at once strikes an observer who has been familiar with its characteristic aspect. Now, I do not know upon what the assertions of some geologists rest, that gravel, moved by water under strong heavy currents, will produce similar effects. ”

“ As it invariably happens that subaerial erosion acts most powerfully along an anticlinal line, the gravels in the hollows and channels would be the longest-preserved from destruction. And we find here and there on the surface of the Boulder-clay patches of this clayey gravel or loam generally capping the higher grounds, frequently many of them in a curved or straight line, showing the direction of the old channel in which they were originally formed. These so-called "Denudation gravels" are never of any great extent or thickness, nearly all having been removed by erosion. ”

“ But it is well known to geologists that a sheet of coarse angular gravel such as this, notwithstanding its looseness, is much less readily attacked by a small stream than is a surface of hard clay or even chalk. Thus plains of Tertiary deposits capped by gravel, under the action of rain or rivers develop into gravel-capped plateaus and hills, which fall abruptly into open flat-bottomed valleys. The denudation takes place at the edge, where the gravel rests on the Tertiary strata and numerous springs are given out ”

“ I have known screw piles to penetrate hard and dense sand, gravel, soft sandy ground, limy gravel, loose silt, limy clay ground something like marl, stiff mud, chalk, clay, marl, and all kinds of water-deposited soil, and in almost every earth except firm rock, but it is not advisable to use them for anything much harder than fine sandy gravel, for the blades must then be strained very much and the pile and screw may be injured. ”

“ The surface of the ground where gravel has been dug is lower only by a few feet, and the beds possibly extend through the ridge. Between the ridge and the higher land to the S.W. a valley intervenes, along which the road to Mildenhall passes, so that the hill on which the gravel reposes is isolated. The gravel is usually not more than 10 feet in thickness, but often less, and it rests in some places immediately on the chalk. It contains a very large proportion of quartzite pebbles from the New Red Conglomerate, in some spots more than 50 per cent. ”

“ These gravels are constantly in movement, being urged forward by the shore currents especially during storms. Large banks of gravel may be swept away in a single night, and in this way the coast is laid bare to the erosive action of the sea. Moreover, the movement of the gravel itself wears down the subjacent rocks. Hence in many places barriers have been erected to prevent the drift of the pebbles and preserve the land, while often it has been found necessary to protect the shores by masonry or cement work. ”

“ As we know the chalk to have been raised from the sea, this upward movement may suggest to us the excavation of the rock by oceanic currents, and the partial deposition of sand; the general accumulation of boulders and clay demands a general disturbance affecting other, and even remote, districts; while the mass of chalk flint gravel seems the natural effect of a more local and less violent convulsion. In some instances, local gravel of this description lies both above and below the proper diluvium. ”

“ The production of sand and gravel from its deposits may be a relatively simple operation or one of considerable complexity. Gravel for surfacing a road may be dug from a conveniently located pit and loaded mechanically into trucks that haul it to the road. A large sand- and gravel-producing operation, however, may include not only mechanical equipment to load and transport the material but also a processing plant where it can be washed if necessary and screened to various sizes. ”

“ On the basis of size, they are called boulders, cobbles, pebbles, and granules. Loose deposits of these larger-size sediments make up what is 12 known as gravel. Nature cements gravels together to form rocks such as conglomerates (made up of rounded gravel) and breccias (made up of sharp-cornered gravel) .
The finer sediments are called sand, silt, mud, and clay. When cemented, the sand grains become sandstones, the silt particles become siltstones, and the mud and clay particles become shale. ”

“ The gravel consists mainly of subangular flints, mixed with some rolled chalk, a considerable number of quartzite pebbles, and rolled fragments of other old rocks, derived from the Glacial Beds higher up the river. It is in a very sandy matrix, more or less ochreous at different spots. In places, the sand predominates.
The Drift-beds rest upon the Gault clay, and not, as in most of the cases already described, upon the Chalk. The implements found here occur usually towards the base of the gravel, and as a rule are rolled and waterworn. ”

“ The bare declivity has evidently been worked, and the auriferous gravel must now be packed from the heights. A barrow with shafts at only one end may be seen beside one of the rockers, and it is conjectured that not all the gravel is picked in buckets. ”

“ 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. ”

“ The gravel used should contain a fair proportion of as large sizes as can be advantageously employed in the particular machine used. Where gravel is not available, crushed stone takes its place. Care should be exercised to obtain stone as strong as the mortar. What proportions of sand, gravel and broken stone should be mixed together is a question determined by the extent of their voids: these may vary from one third to one half the whole volume. Assuming that we have to deal with the larger fraction, a mixture of 1 cement, 2 sand, 4 gravel, should be employed ”

“ 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. ”

“ The Ideal Road Gravel.—The ideal road gravel is a mixture of pebbles, sand and earthy material, the pieces varying from coarse to fine in such a manner that when the gravel is compacted into a road surface the spaces [Pg 81] between the larger pebbles are filled with the finer material. The pebbles are of a variety of rock that is highly resistant to wear so that the road surface made from the gravel will have the quality of durability. The gravel possesses good cementing properties, insuring that the pieces will hold together in the road surface. ”

“ It accumulates in abundance both in stream beds as gravel which has been more or less rounded by wear, and on the hillsides within the soil and sub-soil. Yellow and red iron oxides may stain and penetrate weathered chert gravel so that it becomes reddish, rusty, tan, yellow or brown. ”

“ They do not essentially differ from recent gravel deposits. But in course of time the action of percolating water assisted by pressure tends to convert gravels into firm masses of conglomerate by depositing carbonate of lime, silica and other substances in their interstices. Gravels are not usually so fossiliferous as finer deposits of the same age, partly because their porous texture enables organic remains to be dissolved away by water, and partly because shells and other fossils are comparatively fragile and would be broken up during the accumulation of the pebbles. ”

“ Instead of these tubes there is a layer of some porous material, as gravel, at some distance beneath the surface of the earth, rising at each end and forming a sort of basin (fig. 3) , which is bounded above and below by some impervious substance as clay or stone; the well being sunk at any part (as at a, b, or c) below the level of the gravel, where it forms the surface of the earth, must cut through the upper stratum of clay or stone, and thus form a tube into the porous gravel which holds the water ”

“ But, as the gravel is in general thinly dispersed through the sandstone, and abounds only in some of its layers, it should therefore seem, that a vast body of strata must have been worn away and decomposed, before such quantities of gravel as now exist in the soil could have been let loose. ”

“ I learn more, studying over and over again the same Bagshot sand and gravel heaps, than I should by roaming all Europe in search of new geologic wonders. Fifteen years have I been puzzling at the same questions and have only guessed at a few of the answers. What sawed out the edges of the moors into long narrow banks of gravel? What cut them off all flat atop? What makes Erica Tetralix grow in one soil, and the bracken in another? How did three species of Club-moss—one of them quite an Alpine one—get down here, all the way from Wales perhaps, upon this isolated patch of gravel? ”

“ It goes fast enough at first to carry still coarse gravel; but the big angular blocks of rock have been dropped, and the stones it now leaves in its bed are -55- smaller, and become rounded and smoothed as it goes farther and farther across the plain. At many places it deposits gravel or sand, more especially at the inner side of the curves which the stream makes as it winds down the valley. When the stream runs low in summer, strips of bare sand and shingle are seen at each of these bends; and the stones are always well smoothed and lie on the whole regularly. ”

“ Where rock is scarce and gravel plentiful, the lower layer may be made of the heavier or coarser gravel, leaving the finer gravel for the upper layer, or boxing; but there is no doubt that the broken stone pitching makes the most efficient bottom layer. No gravel ballast should be used which is not free from clay or earthy sand. ”

“ For our gravel-pit, if it be, will possibly yield us another, and a more curious object. You most of you have seen, I dare say, large stones, several feet long, taken out of these pits. In the gravels and sands at Pirbright they are so plentiful that they are quarried for building-stone. And good building-stone they make; being exceedingly hard, so that no weather will wear them away. ”

“ Gravel. —This, if of a flinty character, and not too much mixed with earthy matter, makes good roads for light traffic, if carefully watched or well rolled during formation. Pit gravel should always be screened through wire screens of 11⁄2 to 13⁄4 gauge, and the small can be used for footpaths.
In some places it is difficult to obtain any natural stone for the purposes of road metal; in these cases slag from blast furnaces or ordinary clinkers from furnaces are sometimes used. ”

“ Strata of clay wholly impenetrable by water, often divide beds of gravel that imbibe it freely. There are also cracks that make continuous channels and dislocations that cause them to end abruptly; and there are rents, filled with various materials, that may either give a free passage or entirely bar the underground course of water. Hence, when water has sunk into the earth, it does not by any means soak through it in an equable degree. It is an easier matter for it to ooze many miles, along a layer of gravel, than to penetrate six inches into a layer of clay that may bound the gravel. ”

“ Keeping and myself dug we found there had been a regular displacement of the gravel, and that the beds rose at an angle of thirty degrees, whilst the fossil bed was three feet lower on one side than the other of the pit. In another, after cutting through a foot of gravel, in which we found the os inominatum, of probably Bos longifrons, [12] and a bed of sandy clay about two feet in thickness, we came upon a deposit of gravel about four inches thick, lying in the depressions of the stiff brown clay which succeeded, and in which still remained roots and vegetable matter. ”

“ There the gravel is lighter. Many of the stones are light and rotten; a blow with the pick dashes them to pieces. This streak just above the ledge and for a few inches in the crevices of the ledge is our “pay streak” where ages on ages ago some stream ran, depositing, as all streams do, the heavier gravel on the bottom and the lighter above. Occasionally the pick strikes a firmly embedded boulder hard and square on its point, in such a way as to send the vibration like a shock along the iron, up the handle and into one’s arm and “crazy-bone.” Our bank of dirt is about eight feet in height. ”

“ Abbott to the non-art-producing section of the sewer. The gravels were laid down entirely irrespective of subsequent cutting, natural or artificial; yet we are expected to believe that a so-called gravel man could have resorted for a thousand years to the space a, leaving his half shaped or incipient tools at all stages of the gravel building from base to top, failing entirely to visit a neighboring space b, or to leave there a single flake to reward the most faithful search. ”