Oolite

“ The middle oolite succeeds, which includes the Oxford clay, the Kelloway rock, and the coral-rag, all more or less distinguished by their profusion and peculiarity of fossils, chiefly shells, echini, and corals. The whole formation terminates in two well known deposits, the Kimmeridge clay and Portland oolite, with its bands of green and red sands, layers of chert and drift-wood. This group prevails in Oxfordshire, Berks, Wilts, Bucks, and the Isle of Portland; the matrix of fossilized reptilia, fishes, and cycadeous plants. ”

“ Now this list of fossils is sufficient to mark the oolitic nature of these thick beds below the Cephalopoda-bed of Dorset; and if this new reading of the matter be correct, our sands are not the equivalents of the Gloucester sands, or rather the Cotteswold sands, but the representatives of the lower beds of the Inferior Oolite, which at Ham Hill is a good freestone, from containing so much lime, while at Bradford it is hard, in bands consisting of a shelly oolite, with thick beds of sand between, not sufficiently indurated to be used as stone. ”

“ We have as yet discovered no remains of the leaves, or trunk of Pandaneæ in a fossil state, but the presence of our unique fruit in the Inferior Oolite formation near Charmouth, carries us back to a point of time, when we know from other evidence that England was in the state of new-born land, emerging from the seas of a tepid climate; and shows that combinations of vegetable structure such as exist in the modern Pandaneæ, adapted in a peculiar manner to the office of vegetable colonization, prevailed also at the time when the Oolite rocks were in process of formation. ”

“ The oolitic or Jurassic system, like that of the new red sandstone, comprises the subdivisions of two well-marked natural groups, in which the lias or lower series is included. In point of geographical range, the oolite formation is extensively distributed over the surface of the globe; in mineral character it is varied in every possible degree of texture and composition; in geognostic arrangement there are intercalations, without end, of marine and terrestrial detritus; the organic remains are in the greatest profusion, both as to diversity of type and increase of new creations ”

“ On rock that is much softer than that on the other side of the oolite hills: much softer, because it is much newer. We have got off the oolites on to what is called the Oxford clay; and then, I believe, on to the Coral rag, and on that again lies what we are coming to now. Do you see the red sand in that field?
Then that is the lowest layer of a fresh world, so to speak; a world still younger than the oolites—the chalk world. ”

“ Portland Oolite and Sand (b, Table p. 321) .—The Portland Oolite has already been mentioned as forming in Dorsetshire the foundation on which the fresh-water limestone of the Lower Purbeck reposes (see p. 331) . It supplies the well-known building-stone of which St. Paul’s and so many of the principal edifices of London are constructed. About fifty species of mollusca occur in this formation, among which are some ammonites of large size. The cast of a spiral univalve called by the quarrymen the “Portland screw” (a, Figure 311) , is common; the shell of the same (b) being rarely met with. ”

“ Now if it be assumed that this Cephalopoda-bed at these different points occupies a different horizon, of course we can recognize them as different zones, and name them after their prevailing Ammonites; but it is not so; and it is a remarkable fact that from 2 to 3 feet of the oolite rock in a limited area should present not only so great a crowd of individuals but such a variation in species. ”

“ The Oolite, or Jurassic, underlies the chalk, and overlies the Trias formation. The term “Jurassic” originates from the Jura range, which is almost entirely composed of Oolitic strata. These strata are greatly distorted by pressure, and when we reach Switzerland and the familiar Alps, we find gneiss, crystalline, limestones, and schists, into which the Oolite has [Pg 587] been metamorphosed. The Oolite is divided into Upper, Middle, and Lower, consisting of the following:—
Fig. ”

“ 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. ”

“ Proceeding with our rapid sketch of the crust of the earth and its uses, we now leave the Lias, to enter upon a survey of the Oolite proper. Overlying the Lias, and underlying the Wealden, we find this deposit, which, though it occupies a comparatively narrow track in our own country, is remarkable for the peculiarity and beauty of its fossils, and for the commercial importance of the rocks of which it is composed. ”

“ In parts of Gloucestershire, especially near Minchinhampton, the Great Oolite, says Mr. Lycett, “must have been deposited in a shallow sea, where strong currents prevailed, for there are frequent changes in the mineral character of the deposit, and some beds exhibit false stratification. In others, heaps of broken shells are mingled with pebbles of rocks foreign to the neighbourhood, and with fragments of abraded madrepores, dicotyledonous wood, and crabs’ claws. The shelly strata, also, have occasionally suffered denudation, and the removed portions have been replaced by clay.” ”

“ In a ravine furrowed in the face of the declivity by the headlong descent of a small stream, we may trace all the beds of the system in succession, from the Cornbrash, an upper deposit of the Lower Oölite, down to the Lias, the formation on which the Oölite rests. The only modifying circumstance to the geologist is, that though the sandstone beds run continuously along the cliff for miles together, distinct as the white bands in a piece of onyx, the intervening beds of shale are swarded over, save where we here and there see them laid bare in some abrupter acclivity or deeper water-course. ”

“ Rocks of Bathonian age are well developed in Europe: in the N.W. and S.W. oolite limestones are characteristically associated with coral-bearing, crinoidal and other varieties, and with certain beds of clay. In the N. and N.E., Russia, &c., clays, sandstones and ferruginous oolites prevail, some of the last being exploited for iron. They occur also in the extreme north of America and in the Arctic regions, Greenland, Franz Josef Land, &c.; in Africa, Algeria, German East Africa, Madagascar and near the Cape (Enon Beds) ; in India, Rajputana and Gulf of Cutch, and in South America. ”

“ From this point the oolitic rocks are added to the series, and the formation fills the vale of Isis to Cricklade, turns south to Chippenham, Calne, and Melksham, and, with some interruption in the oolites, continues by Wincaunton and Sturminster toward Ilminster, where it is covered by the Dorsetshire chalk, but reappears on the south side of it about Weymouth. The Portland oolite formation, represented only by the Kimmeridge clay, fills the vale of Pickering in Yorkshire, borders the chalk and lower green sand of Lincolnshire, from the Humber at Ferraby to Spilsby ”

“ Obs.—The difference observable between the lower beds of the Oolite in the midland counties, and those of Yorkshire and Scotland, is a fact of considerable interest. The fluvio-marine accumulations of vegetable matter in the state of coal, with the remains of land-plants at Scarborough and Brora, together with the presence of insects, fresh-water crustaceans, mammalia, and terrestrial plants, in the Stonesfield slate, attest the existence of neighbouring land, and the action of rivers and currents. ”

“ 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. ”

“ The subjacent sedimentary rocks begin with the Cambrian and end with the Inferior Oolite, with a little volcanic tuff with intrusions of diabase and quartz porphyry in the north-east, near Atherstone. ”

“ On the great beds of easily worked Oolite which stretch from Somerset and Wiltshire through Oxfordshire, Gloucestershire and Northamptonshire into Lincolnshire, the work is often both rich and delicate, and has acquired through time and weather a soft grey tint enlivened by the partial incrustation of many-hued lichens. In Derbyshire, Yorkshire, and Lancashire where the stone is much harder, the work is of a plainer and more severe type, such as may be seen at Derwent Hall (Fig. 117) , and the colour is more sombre. ”

“ Finally, from research to research, it is found that perfectly constituted oolites—that is to say, concentric layers, as in the Jurassic limestone—develop themselves in vegetable earth in places where the effects of water in motion is not more admissible than in the preceding instances. ”

“ In the normal order of geological strata, the whole series of cretaceous formations have to be passed through before reaching the Oolite formation, of which the Kimeridge clay forms almost the upper layer. But at Woodhall and the surrounding district the whole of this series of rocks and soils is wanting. Their absence is eloquent, and tells a tale of widespread destruction. ”

“ Judging from what remains, it seems not improbable that the reptiles of this Oolitic period were quite as numerous individually, and consisted of well nigh as many genera and species, as all the mammals of the [Pg 110] present time. In the cretaceous ages, the class, though still the dominant one, is visibly reduced in its standing; it had reached its culminating point in the Oolite, and then began to decline; and with the first dawn of the Tertiary division we find it occupying, as now, a very subordinate place in creation. ”

“ 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 ”

“ Prestwich had ascertained that the valley was bounded on both sides by Oolitic strata, capped by boulder clay, and that the gravel Number 3, Figure 23, contained bones of the elephant, rhinoceros, hippopotamus, ox, horse, and deer, which animals he therefore inferred must have been posterior in date to the boulder clay, through which, as well as the subjacent Oolite, the valley had been excavated. ”

“ The hills close to our encampment are of limestone, which is in many places very angular. Oolite found by Durand in a low range, standing by itself in the valley, it generally bears a vast quantity of nummulites and madrepores. A flat discoid organized remain occurs in abundance, and probably belongs to the same group. Ukko, Rairoo, Kureel rare, Convolvulus spinosus, Frankenioides, Stipaceum gramen, Euphorbia, Polygonum rheoides, Salvadora, may be found. Along the water Andropogonoides 2, Typha, Arundo, Juncus, Scirpus juncinus in abundance. ”

“ This breccia consists of fragments of shale, sandstone, and limestone, with fossils of the oolite, all united together by a calcareous cement. The secondary strata, at some distance from the granite, are but slightly disturbed, but in proportion to their proximity the amount of dislocation becomes greater.
If we admit that solid hypogene rocks, whether stratified or unstratified, have in such cases been driven upwards so as to pierce through yielding sedimentary deposits, we shall be enabled to account for many geological appearances otherwise inexplicable. ”

“ Subdivisions of the Oolitic or Jurassic group — Physical geography of the Oolite in England and France — Upper Oolite — Portland stone and fossils — Lithographic stone of Solenhofen — Middle Oolite, coral rag — Zoophytes — Nerinæan limestone — Diceras limestone — Oxford clay, Ammonites and Belemnites — Lower Oolite, Crinoideans — Great Oolite and Bradford clay — Stonesfield slate — Fossil mammalia, placental and marsupial — Resemblance to an Australian fauna — Doctrine of progressive development — Collyweston slates — Yorkshire Oolitic coal-field — Brora coal — Inferior Oolite and fossils. ”

“ The limestones here found are of various qualities and have never been sufficiently examined, but, from the fossils they contain, which in all are numerous, and of which some entirely consist, they may probably be classed as approximating to the Great oolite of England. ”

“ Even Zamia pectinata may, as Sternberg remarks, have been a fern. Lindley and Hutton place it merely provisionally among the Cycadaceæ, in deference to the judgment of Adolphe Brogniart, and point out its resemblance to Polypodium pectinatum; and a small Helmsdale frond which I have placed beside it bears the impress of a character scarce less equivocal. The flora of the Oolite was peculiarly a flora of intermediate forms. ”