Gravel

“ 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? ”

“ Loose and rattling gravel makes a handsome walk to look at, but an unpleasant one to walk upon. Nothing is more agreeable than well-trodden, dry, root-bound earth, as where grass has been worn away by frequent use ”

“ During the wet season a single rain may fill the gorges, sheet the mountain slopes with water, tear great trees from their hold, break off mighty rock fragments and carry them onward, like wooden blocks, with hundreds of tons of finer gravel. ”

“ Gravel forms a part of those materials which compose our solid land; but gravel is no other than a collection of the fragments of solid stones worn round, or having their angular form destroyed by agitation in water, and the attrition upon each other, or upon similar hard bodies. ”

“ The dirt was well watered and stirred about until all the clay was gone, and then the gravel that remained was emptied into the wash-pan. Now came the anxious moment. All heads were thrust forward to watch. ”

“ 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. ”

“ Where the solid rock has been reached, it has been cut into deep and narrow gorges. Still higher up the valleys, the terraces gradually become more and more broken, narrower, and less thick, until, at a height of from seven to nine thousand feet, they become lost, and blended with the piles of fallen detritus.
I carefully examined in many places the state of the gravel, and almost everywhere found the pebbles equally and perfectly rounded, occasionally with great blocks of rock, and generally distinctly stratified, often with parting seams of sand. ”

“ Consequently, in finding masses of gravel in the composition of our land, we must conclude, that there had existed a former land, on which there had been transacted certain operations of wind and water, similar to those which are natural to the globe at present, and by which new gravel is continually prepared, as well as old gravel consumed or diminished by attrition upon our shores. ”

“ 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 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. ”

“ In places, the gravel is from 12 to 16 feet in thickness, [65] the largest stones, as usual, occurring towards its base, in which part of the gravel the greater number, but by no means all, of the flint implements occur, as some are dispersed throughout the whole thickness of the mass. Occasionally they have been found in pipes of gravel, let down into the chalk by means of water charged with carbonic acid eroding its upper surface. ”

“ Above the grey gravel is a bed of red alluvium, made up of fragments of Jura limestone, in a red argillaceous matrix, in which were embedded several flint knives, with bones of the reindeer and horse, but no extinct mammalia. ”

“ You see all the grains of gravel and sand hurrying down the slope with the water; and if the gravel happens to be coarse, it makes a harsh grating noise as its stones rub against each other—a noise sometimes loud enough to be heard miles away. As the next wave comes curling along, you will mark that the sand and gravel, after slackening their downward pace, are caught up by the bottom of the advancing wave and dragged up the beach again, only to be hurried down once more as the water retires to allow another wave to do the same work. ”

“ Where gravel is the material to complete the road with, I have already mentioned, that it ought to be completely cleansed of every particle of clay or earthy substance, and its different sizes ought to be selected and arranged by means of riddling or washing; in the use of the riddle, the particles of earth or clay adhere so much to the stones that it frequently requires to be exposed to the sun, air, and frost, for several months, and then riddled over again. ”

“ 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. ”

“ Below the chalky gravel, ferruginous beds also sometimes occur, containing large blocks of flint. In the chalky gravel (the base of which is but a few feet above the level of the river) implements are rarely found, but what there are, are usually black. In the upper gravel they are more abundant, and ochreous in tint. It was in this gravel that I had the opportunity of examining one of the cavities already mentioned; and in the pipe formed through the more chalky gravel into which a part of the upper bed had been let down, I witnessed the finding of a pointed flint implement. ”

“ 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; there is scarcely any denudation in the gravel flat, and unless the height of the land is considerable there is no great amount of denudation in the flat bottom of the valley. ”

“ Gravel may be made more compact and will subside if water is pumped upon it and allowed to filter through, and in making an artificial foundation of gravel, it is not reliable without water percolation and consolidation by ramming. ”

“ The unstratified drift may be described as a heterogeneous mass of clay, with sand and gravel in varying proportions, inclosing the transported fragments of rock, of all dimensions, partially rounded or worn into wedge-shaped forms, and generally with surfaces furrowed or scratched, the whole material looking as if it had been scraped together. ”

“ The size of the component pebbles of gravel ranges from great boulders to fine sand, and the finer gravels grade into the coarser sands, the line between gravel and sand being drawn at about the size of a pea, the coarser being gravel, the finer sand. ”

“ 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. ”

“ And when we consider the vastness of the drift-deposits, extending, as they do, over continents, with a depth of hundreds of feet, it would puzzle us to say where were the sea-beaches or rivers on the globe that could produce such inconceivable quantities of gravel, sand, and clay. The production of gravel is limited to a small marge of the ocean, not usually more than a mile wide, where the waves and the rocks meet. ”

“ 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. ”

“ Judging from the section given by Sir Joseph Prestwich, [36] the highest point which the gravel attains is about 59 feet above the river, and its surface in the pit, where the implements are found, is 40 feet above it. The gravel rests upon the Cornbrash, or upper member of the Lower Oolite; but the valley itself, though partly in the limestone rock, has been cut through a considerable thickness of Oxford Clay and of Boulder Clay, which here overlies it. The gravel consists of subangular stones in an ochreous matrix, interspersed with irregular seams of sand and clay. ”

“ Unquestionably, walks near the house should be graveled; they naturally have too [175] hard usage to keep turf in good condition. Graveled walks should be dug out a foot or more in depth, filled in with broken stone, this covered well with coarse gravel, and finished with a coating of a couple of inches of whatever fine gravel is chosen. ”

“ On the west, gravel beds lie against rock and till; on the east, deposits of sand and coarse gravel form a bench or terrace from 500 to 700 feet broad, which after following the side of the valley for one-half mile, crosses it diagonally and joins the western slope as a row of rounded hills. Through this drift the present stream has cut a narrow channel. ”

“ They called Anthea 'Panther', which seems silly when you read it, but when you say it it sounds a little like her name.
The gravel-pit is very large and wide, with grass growing round the edges at the top, and dry stringy wildflowers, purple and yellow. It is like a giant's wash-hand basin. And there are mounds of gravel, and holes in the sides of the basin where gravel has been taken out, and high up in the steep sides there are the little holes that are the little front doors of the little sand-martins' little houses. ”

“ Q. Why is a gravel walk almost dry, when a grass plat is covered thick with dew?
A. Grass, (being a good radiator) throws off its heat very freely; but gravel (being a very bad radiator) parts with its heat very reluctantly.
Q. Is that the reason why grass is saturated with dew, and the gravel is not?
A. Yes. When the vapour of warm air comes in contact with the cold grass, it is instantly chilled into dew; but (as the gravel is not so cold as the grass) the vapour of air is not so freely condensed as it passes over the gravel.
Q. Why does dew rarely fall upon hard rocks and barren lands? ”

“ 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. ”

“ This country having no high mountainous part in the middle, so as to give it a considerable declivity towards the shores and rivers, the gravel has remained in many places, and in some parts of a considerable thickness. But in other parts of the island, where the declivity of the surface favours the transportation of gravel by the currents of water, there is less of the gravel to be found in the soil, and more of the fragments of stone not formed into gravel. ”

“ In some places deep excavations were made before gravel could be obtained to form the surface of the road; and from the swampy nature of the ground much draining was required to render the foundation solid and the line durable. The danger of sinking in boggy ground for gravel was often felt. Once in particular when the party had dug to the depth of fourteen feet in a broken morass, the sergeant (Read) observed the whole mass of moss in motion. Instantly he ordered the workmen to leave the pit.pit. ”

“ 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. ”

“ Underneath the peat is a bed of gravel, a, from 3 to 14 feet thick, which rests on undisturbed Chalk. This gravel was probably formed, in part at least, when the valley was scooped out to its present depth, since which time no geological change has taken place, except the growth of the peat, and certain oscillations in the general level of the country, to which we shall allude by and by. A thin layer of impervious clay separates the gravel a from the peat Number 1, and seems to have been a necessary preliminary to the growth of the peat. ”

“ The greater part of the hill is capped with gravel, in places from 8 to 10 feet thick, and of much the same character as that at Gravel Hill, but less ferruginous, and not containing so many quartzite pebbles. The beds here have not been excavated to the same extent as those near Brandon, the gravel being only dug for the repairs of the parish roads; but several well-fashioned implements have been found in them, mostly of pointed form. ”