Oolitic limestone

“ Of the five formations which compose the oolitic system in England, the upper or wealden formation is the most local the lower or lias formation the most extensive: the three intermediate or properly oolitic formations are easily distinguishable in the south of England and the north of France; but in the south of France, and generally in the Jura mountains, from Geneva to Bayreuth, this discrimination is a work of difficulty. Even in England, the three oolitic are not coextensive, at least their calcareous portions: the upper or Portland limestone is the most limited and interrupted ”

“ Oölitic limestone (oolite) .—This rock is made up of spherical nodules and so has the appearance of fish roe. Broken apart, each grain reveals in its center a core of siliceous sand about which carbonate of lime has been deposited in concentric layers. It is thought that waters charged with carbonate of lime, in issuing from a river near a sea beach, coat the sand grains of the latter with successive thin films of lime carbonate due to the rhythmic ebb and flow of the tides, evaporation of the adhering water taking place when the sands are exposed at low tide. ”

“ In the deeper valleys, towards the eastern edge of these sandstones thin beds of oolitic limestone, containing numerous fossil shells, occasionally occur; also gypsum and clayey shales, with other indications of the probable existence of coal in the vicinity; following the series appears a compact, fine-grained amorphous sandstone, having an almost flinty fracture; this rock, in a few miles, gives place to granite and gneiss, frequently broken up by the upheaval of whinstone and porphyritic trap hills, having an elevation of from 100 to 500 feet above the plain. ”

“ Limestone becomes granular and saccharoid—it is changed into marble. The [73] most remarkable instance of this metamorphism is the Carrara marble, a non-fossiliferous limestone of the Oolite series, which has been altered and the fossils destroyed; so that the marble of these celebrated quarries, once supposed to have been formed before the creation of organic beings, is now shown to be an altered limestone of the Oolitic period, and the underlying crystalline schists are sandstones and shales of secondary age modified by plutonic action. ”

“ Stonesfield Slate: Mammalia.—The slate of Stonesfield has been shown by Mr. Lonsdale to lie at the base of the Great Oolite. [5] It is a slightly oolitic shelly limestone, forming large lenticular masses imbedded in sand only six feet thick, but very rich in organic remains. It contains some pebbles of a rock very similar to itself, and which may be portions of the deposit, broken up on a shore at low water or during storms, and redeposited. The remains of belemnites, trigoniæ, and other marine shells, with fragments of wood, are common, and impressions of ferns, cycadeæ, and other plants. ”

“ In texture, a few limestones are compact, some oolitic, many cellular, the cells lined with crystallised carbonate of lime, a large proportion of a fine sandy grain, some quite powdery, with crystallised balls included; and in Nottinghamshire, considerable tracts yield granular crystallised limestones. Near Sunderland laminated rocks are really of sparry texture. Strings and plates of spar are very common, and render buildings of the magnesian limestone very irregular in their decay, from the unequal perishing of the stone between the ribs of spar. ”

“ This ridgy prominence is due to the solidity of the rock, and to the softness of the shales above and below it. Near Wenlock it consists of thick masses of grey subcrystalline limestone, replete with corals, encrinites, and trilobites. It is essentially of a concretionary nature; and the concretions, termed “ball-stones” in Shropshire, are often enormous, even 80 feet in diameter. They are of pure carbonate of lime, the surrounding rock being more or less argillaceous [2] Sometimes in the Malvern Hills this limestone, according to Professor Phillips, is oolitic. ”

“ Lias, a set of strata variously composed of limestone, clay, marl, and shale, clay being predominant; 2. Lower oolitic formation, including, besides the great oolite bed of central England, fullers’ earth beds, forest marble, and cornbrash; 3. Middle oolitic formation, composed of two sub-groups, the Oxford clay and coral rag, the latter being a mere layer of the works of the coral polype; 4. Upper oolitic formation, including what are called Kimmeridge clay and Portland oolite. ”

“ A stratified rock belonging to the Carboniferous group. See Table L, p. 393.
Olivine. An olive-coloured, semi-trans_parent, simple mineral, very often occurring in the forms of grains and of crystals in basalt and lava.
Oolite, Oolitic. A limestone, forming a characteristic feature of a group of the secondary strata. See Table II. H, p. 391, It is go named, because it is composed of rounded particles, like the roe or eggs of a fish, Etym.,oon, egg, and lithos, stone.
Opalized wood. Wood petrified by siliceous earth, and acquiring a structure similar to the simple mineral called opal. ”

“ Mr. Granville Penn, however, gets over the difficulty of the cave, which is hollowed, I may mention, in a limestone of the Oolitic series, inclosing the ammonite and belemnite, by asserting that its mammaliferous contents may be somewhat older than itself! The limestone existed, he holds, as but a mere unformed pulp at the time the intertropical animals came floating northwards: they sank into it; the gasses evolved during putrefaction blew up the plastic lime above them into a [Pg 333] great oblong bubble, somewhat as a glass-blower blows up a bottle ”

“ The deposit of carbonate of lime, which took place under circumstances that caused it to attract around its nodules the organic particles, whence the name oolite (egg-stone) is derived, was not continuous, but repeated at intervals. The shells of Mollusks were developed in great abundance, and accumulations of these formed thick bands, which consolidated into layers of shell-limestone. Three hundred feet of strata, largely composed of organic remains, were formed before the clay was deposited which made the Stonesfield and contemporaneous slates. ”

“ He told me that some specimens of it, which he had collected and brought home, were treated by his brother, a professed mineralogist, as specimens of carboniferous limestone. The formation of oolites, again, may be studied at the present time. When a bed of calcareous sand, formed by the wearing down of shells or corals, is raised above the sea-level, and is penetrated by rain-water charged with carbonic acid, this, dissolving the carbonate of lime of the surface-layer, deposits it again around the grains of the deeper layers, which it invests with concentric coats. ”

“ Those which appear in considerable thickness, as the Bath oolite, Portland oolite, Oxford oolite, are generally of the oolitic texture in the middle, though below and above this may be exchanged for compact or shelly beds. Thin detached limestones, like the forest marble, are sometimes very coarsely oolitic: calcareous layers in sand are usually charged with siliceous matter and often cleave able to slate or flags (Stonesfield) . The grains of oolite vary much in size; the smallest are perfectly spherical, the largest irregular; they generally cohere ”

“ In mountainous districts limestones are often recognizable by these peculiarities. The chalk downs are celebrated for the close green sward which they furnish. More impure limestones, like those of the Lias and Oolites, contain enough insoluble mineral matter to yield soils of great thickness and value, e.g. the Cornbrash. In limestone regions all waters tend to be hard, on account of the abundant carbonate of lime dissolved by percolating waters, and caves, swallow holes, sinks, pot-holes and underground rivers may occur in abundance. ”

“ For building purposes, the fine-grained oolites without large fossils are much sought after, since they can be trimmed equally in any desired direction.
Before leaving the question of the inorganic deposition of limestone, we may note that R. A. Daly [7] has suggested that the pre-Cambrian and early Cambrian limestones were entirely products of chemical precipitation. He believes that the continental - 19 - areas were at first relatively small, and that the abundance of decaying soft-bodied organisms on the sea-floor led to a continuous precipitation of such calcium carbonate as was available. ”

“ A soft shelly limestone, most probably of recent origin though slightly resembling some of the oolites of England, occurs extensively on the southern coast between Cape Northumberland and Portland bay where it forms the only rock with the exception of amygdaloidal trap. ”

“ They were formed under water, and clay and sand were laid down with the lime in such quantity in some cases that the resulting stone is not worth handling for soil improvement. A stone that is practically all carbonate of calcium, or a combination of calcium and magnesium, is wanted because it is these two elements that give value to the material. If a poor stone is used, too much waste matter must be handled. Twenty-five per cent more ground limestone of 80% purity must be applied than would be required in the case of an absolutely pure limestone. ”

“ Oblique lamination belongs to many of the coarse shelly oolites: spongoid bodies, enveloped in siliceous matter, lie in the oolitic rocks of Portland and Oxford, but not so regularly as flints do in chalk: there is very little pyrites, and, except in the lower Bath oolite, little oxide or carbonate of iron in the calcareous rocks, above the lias. ”

“ If we admit what is perhaps impossible to be denied that the production of each sort of rock spread from some centre, and that these centres were not coincident for different rocks, it becomes a very curious problem to determine what are the lines of contemporaneity in the oolitic system.
For let A be a point from whence a deposition of carbonate of lime spreads slowly through the ocean, but not reaching to B, a point from which depositions of sand happen, not reaching to A—the general basis r, r, r, being red marl and sandstone. ”

“ Where oxide of iron forms the cementing material, the rock yields less readily to weathering, and the sandy soil will be yellowish brown or red according to the climate. Another simple case is that of limestone which when perfectly pure yields no soil because it is all soluble. Pure limestone is, however, rare, and the various mineral impurities in it, being to a considerable degree insoluble, tend to remain to form a residual soil which may vary from sandy to clayey, and usually brown or red due to the setting free of oxides of iron. ”

“ The next great calcareous formation above the Oolite is the Chalk, the material of which is exactly the same as that of limestone, although its texture is so different. Our deep-sea researches have entirely confirmed the opinion which had been previously formed on the basis of microscopic research, that the whole of the enormous mass of Chalk now raised up into the cliffs and downs of the southern portion of England was formed on the bed of the ocean, by the agency of animals—chiefly the minute Foraminifera, which separate carbonate of lime from the seawater as the material of their shells ”

“ Now, in later formations, limestone is usually an organic rock, accumulated by the slow gathering from the sea-water, or its plants, of calcareous matter, by corals, foraminifera, or shell-fish, and the deposition of their skeletons, either entire or in fragments, in the sea-bottom. The most friable chalk and the most crystalline limestones have alike been formed in this way. We know of no reason why it should be different in the Laurentian period. ”

“ The day would come when the surface soil could not produce our staple crops if its loss of lime continued, and a means of replenishing the stock were not at hand. The huge deposits of limestone that have not been disintegrated by processes of weathering are assurance that the soil's need can be met forever. The calcium and magnesium in the stone are in chemical combination with carbonic acid forming carbonates, and there is an additional mixture of other earthy material that was deposited by the water when the stone was being formed, but much limestone possesses an excellent degree of purity. ”

“ There the amount of evaporation is often sufficient to cause a re-deposit of the mineral in solution. If it be lime, a white crust gathers along the sides of the stream, delicately enveloping grass-stalks, leaves, twigs, snail-shells, and other objects, which it may meet with in its progress. Such "petrifying" springs, as they are popularly termed, occur abundantly in our limestone districts. It should be borne in mind, however, that they only produce an incrustation round the organic nucleus, and do not petrify it. ”

“ It may therefore be considered as a discovery of some importance, that we possess, in this country, a species of limestone which, when used for purposes of extracting lime, and in the preparation of mortar, is capable of communicating to the cement all the properties of the pulvis Puteolanus. ”

“ The lakes disappeared, and above their deposits, as above the rest of England and nearly all Europe except Scandinavia and patches of Spain, Italy, and the Balkans, a deep ocean rolled, and for many thousands of years deposited a grey ooze of limestone. This limestone is called the Carboniferous or Mountain Limestone. But as time went on this old sea floor began to be slowly raised, and in the shallower waters a great quantity of coarse sand and stones and conglomerate—the Millstone Grit, as it is called—was deposited. ”