Chalk

“ Composition and Uses.—In the Andover district Chalk Compost or “Chalk Mud,” as it is called locally, is prepared and used as follows:
The chalk is dug out in the autumn, and the frost allowed to play on it during the winter. In the spring building starts, and the weathered chalk is spread all around the outside of the walls. Straw is sprinkled on it and it is then well trodden, usually by the workers, but sometimes by horses. Sometimes chopped straw is added, sometimes unchopped straw is sprinkled on. ”

“ Chalk is not rich and fertile, like manure, it is altogether poor, barren stuff: you know that, or ought to know it. Recollect the chalk cuttings and banks on the railway between Basingstoke and Winchester—how utterly barren they are. Though they have been open these thirty years, not a blade of grass, hardly a bit of moss, has grown on them, or will grow, perhaps, for centuries. ”

“ If you will look at the surface of the chalk, where the sands and clays lie on it, you will find that it is not smooth; that the beds do not rest conformably on each other, as if they had been laid down quietly by successive tides, while the chalk below was still soft mud. ”

“ Chalk, as a source of lime, has always been of high importance to builders, and, until improved transport brought alien materials into its old preserves, chalk was in general use for walling in the form of roughly squared blocks. ”

“ The middle and upper strata consist of chalk of extreme whiteness and purity, and are chiefly distinguished from each other by the upper one containing layers of flint nodules which do not occur in the lower. The chalk without flints is most frequently somewhat harder than that with flints, and hence they are sometimes distinguished as the hard and soft chalk ”

“ The White Cliff is composed of a cap of chalk, a hundred feet thick, striated with beds of flint, and this rests on a series of shelving cherty sandstone beds of a tawny hue. The inclination of these gives to the whole headland an appearance of lurching to its fall.
Water sinking through the chalk oozes through the sand and dissolves it, undermining the white bed above till masses of chalk that have lost all support hurtle down. But the chalk itself is full of cavosities caused by the soft rock being eaten into by the sea-winds. ”

“ The perfect state of the surfaces of the chalk fossils proves also that this deposition proceeded from the surrounding fluid, and that it was not derived from the immediate action of any chemical agent, on the shells and other calcareous coverings of the animals living at the bottom of the sea. In the fossil animal bodies found in chalk, not the least diminution of the sharpness of their ridges or points is observable, nor is the least dulness of the delicate lines and embossments of the crusts, or of the spines of the echini, to be detected. ”

“ But on our southern coasts, the wall-sided cliffs, many hundred feet high, with vast needles and pinnacles standing out in the sea, sharp and solitary enough to serve as perches for the wary cormorant, confer a wonderful beauty and grandeur upon the chalk headlands. And in the East, chalk has its share in the formation of some of the most venerable of mountain ranges, such as the Lebanon. ”

“ At first the young men keep their eyes rigidly closed or even sealed with a plaster of chalk, and they appear not to understand the words of command which are given them by an elder. Gradually, however, they come to themselves as if awakening from a stupor, and next day they bathe and wash off the crust of white chalk with which their bodies had been coated. ”

“ The chalk of England, although it appears upon the surface only in detached hills and patches, is actually continuous through considerable tracts of country, where it exists at great depths, as is now ascertained by numerous wells and other sinkings. In the order of position, which the strata of the chalk itself, and those which lie above and below it, bear severally to one another, there has been observed in distant places a remarkable agreement. ”

“ A white fossil substance, by some reckoned a stone, but of a friable kind, which cannot, therefore, be polished as marble; by others, more properly ranked among the earths. It is of two sorts, one a hard dry chalk, used for making lime; the other a soft, unctuous kind, used in manuring land, &c. Chalk always contains quantities of flint-stone, and the fossil remains of shells, coral, animal bones, marine plants, &c.; from which circumstance there can be no doubt that chalk is the deposited mud of a former ocean. The chemical name of chalk is carbonate of lime. ”

“ In tracing this vast collection of water-worn materials, we find that it forms a considerable hill behind the town, and that it joins to the side of the range of hills called the South Downs.
In Alum bay in the Isle of Wight, however, the stratum immediately next to the flinty chalk, and consequently deposited upon it, consists of a white chalk marl without flints. Its nature is sufficiently shewn by its pulverizing with the frost; and the rains wash it down, so that its situation is marked by a deep hollow. ”

“ No better illustration can be found than the white earthy limestone, familiar to every one under the name of chalk. An undulating stratum of Chalk Rock, attaining not unfrequently a thickness of one thousand feet, may be said, speaking roughly, to underlie the southeastern half of England. ”

“ In these cavities we recognize an exact counterpart to those which are so numerous on the furrowed surface of our own white chalk. Advancing from these quarries along a road made of the white limestone, which reflects as glaring a light in the sun, as do our roads composed of chalk, we reach, at [p.189] length, in the neighbourhood of Aurillac, hills of limestone and calcareous marl, in horizontal strata, separated in some places by regular layers of flint in nodules, the coating of each nodule being of an opaque white colour, like the exterior of the flinty nodules of our chalk. ”

“ To a thinking mind few phenomena are more strange than the state of little ponds on the summits of chalk hills, many of which are never dry in the most trying droughts of summer. On chalk-hills I say, because in many rocky and gravelly soils springs usually break out pretty high on the sides of elevated grounds and mountains: but no person acquainted with chalk districts will allow that they ever saw springs in such a soil but in valleys and bottoms, since the waters of so pervious a stratum as chalk all lie on one dead level, as well-diggers have assured me again and again. ”

“ If we follow the lines of fault, we may see, says M. Puggaard, along the planes of contact of the shifted beds, the marks of polishing and rubbing which the Chalk flints have undergone, as have many stones in the gravel of the drift, and some of these have also been forced into the soft Chalk. The manner in which the top of some of the arches of bent Chalk have been cut off in this and several adjoining sections, attests the great denudation which accompanied the disturbances, portions of the bent strata having been removed, probably while they were emerging from beneath the sea. ”

“ It is true, chalk is not in so general use, as an article of diet, as cheese, except in boarding-schools; but the difference is plainly one of degree rather than of kind. We have heard of "prepared chalk." It has been whispered that gentle spinsters use it for a beautifyer. We rather incline to the belief that it is prepared for the inside rather than the outside of humanity. ”

“ This fact is also in accordance with the hypothesis, for the river at the time of the formation of these lower beds would, in the lower part of its course, have completely cut through the Glacial deposits above the Chalk, and would have been attacking the Chalk itself. There is also an abundance of rolled chalk in the Shrub Hill beds, which seem to be of much the same age. In the valley of the Lark, the rolled chalk pebbles occur in gravels at a somewhat greater elevation. ”

“ In England every part of our chalk is completely covered by vegetable soil, which although very thin on many parts of our downs or smooth hills, yet affords support to peculiar grasses and other vegetables, on which are pastured vast quantities of sheep. The chalk of Franco is said to contain 11 per cent. of magnesia, to which the barrenness may be owing. ↑ On the authority of Mr. Parkinson I notice that the supposition of having discovered a specimen of Trigonia in chalk is erroneous. This belongs only to inferior strata. ”

“ Infinitesimal specks, often so minute as to appear only as fine dust to man’s unaided sight; yet real organic remains, each one of which has been the home of an active animal.
A lump of chalk is a mass of densely packed [p. 139] tiny fossil shells, more or less crushed and broken. It has been reckoned that a cubic inch of chalk probably holds at least one million shells.
Try to imagine what this means. The work of the Ocean in building solid sandstone, from unnumbered myriads of myriads of grains of sand, is marvellous enough. But here we have something far more wonderful. ”

“ As the little creatures die in the sea, their shells accumulate on the bottom, and in time will be pressed into a hard mass like chalk, the whole being cemented together by carbonate of lime, in the way we explained in describing the making of limestones. So we find chalk still forming at the present day. But what ages it must take to form strata of solid rock of such tiny shells! And what a vast period of time it must have required to build up our chalk cliffs and downs, composed in large part of tiny microscopic shells! ”

“ Thus the chalk is no unimportant element in the masonry of the earth's crust, and it impresses a peculiar stamp, varying with the conditions to which it is exposed, on the scenery of the districts in which it occurs. The undulating downs and rounded coombs, covered with sweet-grassed turf, of our inland chalk country, have a peacefully domestic and mutton-suggesting prettiness, but can hardly be called either grand or beautiful. ”

“ In such cases we sometimes discover that the more modern rock has been in part derived from the degradation of the older. Thus, for example, we may find chalk in one part of a country, and in another strata of clay, sand, and pebbles. If some of these pebbles consist of that peculiar flint, of which layers more or less continuous are characteristic of the chalk, and which include fossil shells, sponges, and foraminifera of cretaceous species, we may confidently infer that the chalk was the oldest of the two formations. ”

“ The Chalk comprises all the main divisions of the formation, including the Totternhoe stone, Melbourn rock and Chalk rock. Much glacial boulder clay covers all the higher ground of the county; it is a stiff brownish clay with many chalk fragments of travelled rocks. Near Ely there is a remarkable mass of chalk, evidently transported by ice, resting on and surrounded by boulder clay. Plateau gravel caps some of the chalk hills, and old river gravels occur at lower levels with the bones of mammoth, rhinoceros and other extinct mammals. ”

“ Chalk is found in regularly stratified and separated masses, sometimes caused by beds of flints, and although the position of the layers may indicate their successive ages, age can hardly be taken as an absolute indication of the increased stability of chalk in earthwork. When overlaid with clay it is usually harder than when bare, probably owing to pressure, non-exposure to atmospheric influences, and to the absorbed water being of a different character, which has been proved by analyses. ”

“ The species of all these, and of other fossils, in the chalk-pit and in the gravel-pit, are absolutely identical. The natural conclusion is, then, that the gravel has been formed from the washings of the chalk. The white lime of the chalk has been carried away in water by some flood or floods; the heavier flints have been left behind.
Stop now one moment, and think. You all know how very few flints there are in the chalk-pit, in proportion to the mass of chalk. You all know what vast gravel-beds cover the country to the north, and often to the thickness of many feet. ”

“ The hard chalk lies immediately beneath the soft chalk. In this stratum there are no flint nodules. “ Its beds,” according to Mr. Farey, “ increase in hardness, until near the bottom where a whitish freestone is dug, at Totternboe in Bedfordshire, and at numerous other places; that brought from Ryegate and other quarries, of this stratum, south of London, is used as a fire-stone.” [11]
It has been generally supposed that these two strata of chalk are of one formation: but not only the absence of the flints, but the characters of their fossils prove them to be of distinct formations. ”

“ As a pigment, chalk possesses many valuable properties. The organic structure of chalk gives it high covering power as a wash, a thin layer applied to a surface sufficing to mask the colour of the underlying ground completely. The lime in chalk being combined with carbonic acid, its basic properties are so extensively weakened that chalk can be mixed with even the most delicate colours without fear of their shade being affected. A coating of pure chalk paint on any surface will never change colour in the air ”

“ In the upper chalk every one has seen the layers of flint, and marked their singular distribution, in layers; and here we would add, that the existence of flint in chalk is one of those hard nuts which geology has not yet cracked. The geologist, the chemist, and the zoologist have all puzzled themselves in vain to find a truly satisfactory origin for these nodules of siliceous matter. ”