Oolitic

“ 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. ”

“ In places also, as in Yorkshire and Sutherlandshire, are found actual beds of coal: but the great bulk of the formation is an indubitable sea-deposit; and its limestones, oolitic as they commonly are, nevertheless are composed largely of the comminuted skeletons of marine animals. Owing to the enormous number and variety of the organic remains which have been yielded by the richly fossiliferous strata of the Oolitic series, it will not be possible here to do more than to give an outline-sketch of the principal forms of life which characterise the Jurassic period as a whole. ”

“ But not a few of the Oolitic plants in Scotland bear this modern aspect. The great development of its Cycadaceæ,—an order unknown in our Coal Measures,—also forms a prominent feature of the Oolitic flora. One of the first known genera of this curious order,—the genus Pterophyllum,—appears in the Trias. It distinctively marks the commencement of the Secondary flora, and intimates that the once great Palæozoic flora, after gradually waning throughout the Permian ages, and becoming extinct at their close, had been succeeded by a vegetation altogether new. ”

“ Another example of the value of Ichthyology, in illustration of Geology, occurs in the fact, that as the fossil Fishes of the Wealden estuary formation are referable to genera that characterize the strata of the Oolitic series, the Wealden deposites are hereby connected with the Oolitic period that preceded their commencement, and are separated from the Cretaceous formations that followed their termination. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ In the oolitic series, therefore, where the several strata are developed in conformity with the more ordinary type of these formations, we may venture to predict with certainty, that no carboniferous deposits of any great value will ever be discovered, at all events in Great Britain. A want of such knowledge has induced many persons to make trials for coal in beds subordinate to the English oolites, and even superior to them, in places where the type of formation did not offer the least warrant for such attempts. ”

“ No true fossil palms have yet been detected in the great Oolitic and Wealden systems, though they certainly occur in the Carboniferous and Permian rocks, and are comparatively common in the earlier and middle Tertiary formations. Much cannot be founded on merely negative evidence ”

“ The oolitic and cretaceous periods appear to have been scarcely broken by any violence in the region of the British isles, but the whole bed of the sea underwent a gradual and continual rise, which brought up progressively the north-western parts of the oolitic rocks. (On the continent of Europe the oolitic and cretaceous periods were divided by an interval of great disturbance.) ”

“ 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. ”

“ 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. ”

“ The various calcareous deposits in the mountain limestone, magnesian, oolite, and chalk periods, would imply very different qualities in the condition of the ocean; an infusion or abstraction of ingredients as favorable to the existence of one kind of animal life as they would be destructive of another. A period of great plutonic action, too, when vast masses of melted matter, charged with metallic and other substances, were poured over the bed of the sea, could not fail to have considerable influence upon many of the inhabitants of the deep ”

“ A small percentage of siliceous materials occurs in the ooze, made up partly of granules of quartz, and partly of the skeletons and coverings of minute animal and vegetable organisms. When in process of time the chemical forces begin to act upon the siliceous matter diffused through the Atlantic ooze, segregation, or the gathering together of the particles, may take place, and nodules of flint will be the result, similar to the flint nodules which occur in chalk, and the cherty concretions in limestones. ”

“ We have seen, for instance, that Coal is the representative to our age of swamps and forests which once covered the earth with vegetation; that Mountain Limestone is in great part formed from the skeletons of reef-building corals; that the White Chalk of Europe is almost entirely derived from the remains of marine shells. But it should be observed that these and such like rocks, while they afford us much valuable information about the ancient organic condition of our planet, are not, strictly speaking, Fossil Remains. ”

“ 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. ”

“ As the fundamental earths lose themselves in pure carbon, in resin, and so in the vegetable world, so the series of corrosive earths resolves itself likewise in remnants of an organic, and that indeed the animal, kingdom. As the pit-coals and resins are associated with the metals and Inflammables, so are the fossil animal remains with the calcareous earth; and thus the voice of the organic world speaks already with force and clearness to those that hearken, from out the stones. ”

“ 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. ”

“ If we imagine a world altogether destitute of life, we still might have geological formations in progress. Not only would volcanoes belch forth their liquid lavas and their stones and ashes, but the waves and currents of the ocean and the rains and streams on the land, with the ceaseless decomposing action of the carbonic acid of the atmosphere, would be piling up mud, sand, and pebbles in the sea. There might even be some formation of limestone taking place where springs charged with bicarbonate of lime were oozing out on the land or the bottom of the waters. ”

“ That the Earth was once as hot on its surface as it now is underneath, we know from the condition of the plutonic rocks where sedimentary strata have not covered them up. Volcanoes and geysers are our only avenues now to that earlier state of things. From these pathways to the past, and only from them, do we find elementary substances produced to-day,—hydrogen, sulphur, chlorine, oxygen, and carbon. [1] We are thus made aware that once the Earth was simple, too, on the surface as well as deeper down. ”

“ Nothing is in the sedimentary rock that was not at one time in the original granite, or in the primordial seas, or in the primordial atmosphere, or in the heavens above, or in the interior of the earth beneath. We must sweep the heavens, strain the seas, and leach the air, to obtain all this material. Evidently the growth of these rocks has been mainly a chemical process—a chemical organization of preexisting material, as much so as the growth of a plant or a tree or an animal. ”

“ The Eolian or Aërial group of rocks embraces all natural accumulations of organic or inorganic materials, which have been formed upon the land. The group is typically represented by débris, such as gathers on hill-slopes and at the base of cliffs, by the sand-hills of deserts and maritime districts, and by soil. All these accumulations owe their origin to atmospheric agencies, as will be more particularly described in the sequel. ”

“ The atmosphere of that early day, filled with vast volumes of carbon, oxygen, and other chemicals that have since been stored in beds of coal, limestone, and granites, may have worn down the rocks on the one hand and built up organic forms on the other, with a rapidity that would now seem hardly conceivable. ”

“ Animals and plants contribute to the formation of rocks in three distinct ways:—
1. During their growth they deoxidize carbon dioxide and water, and reduce to the solid state in their tissues carbon and the permanent gases oxygen, hydrogen, and nitrogen; and after death, through the accumulation of the half-decayed tissues in favorable localities,—marshes, etc.,—these elements are added to the solid crust of the earth in the form of coal and bitumen. ”

“ With the separation of the ore and the Inflammable out of the primary water and the confluence of the Earthy into marine salt, its metamorphosis upon the surface or when exposed to light is at an end. All forms of the planet have been successively developed out of the earth-element. It can attain no further to anything new, and if nature had not yet been concluded, that which in the sequel is still dynamically developed upon our earth, must be thus a product, which extends beyond the mineral kingdom. ”

“ Although the gaseous matter first absorbed would soon be condensed, and part with its heat, yet the continual arrival of fresh supplies from below might, in the course of ages, cause the temperature of the water, and with it that of the containing rock, to be materially raised; the water acts not only as a vehicle of heat, but also by its affinity for various silicates, which, when some of the materials of the invaded rocks are decomposed, form quartz, feldspar, mica, and other minerals. ”

“ If it were otherwise—if the same species abounded in every climate, or in every part of the globe where, so far as we can discover, a corresponding temperature and other conditions favourable to their existence are found—the identification of mineral masses of the same age, by means of their included organic contents, would be a matter of still greater certainty. ”