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Marls and marly
Connected by alternations with the siliceous limestone.
III. First Local Fresh-water, or Brackish-water Deposit.
S. E. Of
Austrian, MoRav., Hcngar. I&transylv.b. Blue clay (syn. Tegel). shelly, selenite In the upper part melan opside
molasse oil Fragments of
|Not present in
-\ short beds, Bre-
Trachytic con- \
glomerate, ( beds, Pumice conglo- t Hungary.
CLASS IV—TERTIARY ROCKS,-Continued.
STRATIFIED OR NEPTUNIAN ROCKS.
IV. Second Tertiary Arenaceous And Calcareous Formation.
Sometime* Marine FottiU.
V. Last Frcsh-uuter Deposit. Local Fresh-water deposits, formed by springs or basins of fresh-water at very different periods of time.
N. B. Tertiary rocks exist in the steppes of Asia, in India, in Africa, in the Canaries, Island of Madeiria, and the West Indian Islands (Guadalouiie, Barbadoes, (fee), in Columbia, and in the Atlantic United States.
Sandy and marly shelly marine deposit. Local Shells still living in the same
deposits above the sea level. countries, and not altered.
Shelly marls, in Scandinavia;—shelly sand, near Nice;—shelly marl, with oysters, near La Rochelle:—
NEW ALLUVIAL FORMATION.
New alluvium of rivers,—consisting of rolled stones, sand, clay, &c.
Deposits from water -pisolithes, sulphur (Baden, Austria^ bog iron-ore, calcareous tuff of Baden (calcaire d'eau
Peat-bogs,—phosphate of iron.
The various substances produced by sublimation
The various substances produced by the solfa-
IV. After taking a view of the structure and arrangement of the crust of the earth, it is almost impossible to avoid forming some theory to explain the mode by which it was brought to its present habitable condition. Almost every appearance it presents informs us that it has undergone mighty revolutions: the regularly formed horizontal strata of some formations are similar to the arrangements of those mechanical deposits from water which at present come under our observation; and the crystalline structure of others forces us to infer a liquidity, by which only, according to the present laws of nature, that structure could be produced. The globular form of the earth is a sufficient proof that it was once liquid, because the liquid condition only could have allowed it to assume such a shape. The occurrence of petrified sea-shells, and of the petrified remains of fishes on high mountains, is also a certain evidence that the waters must at one time have risen beyond their present level, and that these eminences were of posterior formation to the animals whose exuviae they enclose. When petrified bones and horns of land animals are found in fossils, the same inference may legitimately be made. The immense quantities of mineral coal found in the bowels of the earth, and the connexion that may be traced betweeri it and moss, or the remains of plants decaying under our observation, carry us back to a luxuriant vegetation before the period when our present soil was formed, or perhaps before the crust was arranged that supports it
It is needless to multiply examples where general appearances are so striking, or to engage in abstruse reasoning where inferences are so easily drawn. Indeed, without any induction of facts, but what a very superficial experience affords, every one almost is compelled, from existing phenomena, to form some hypothesis; and that hypothesis will be more or less rational, according as it is suggested by a greater or smaller number of observations, and explains consistently a greater or smaller number of facts. There can be no presumption in tracing the laws of Nature through her most magnificent operations, any more than through her most minute, provided we strictly adhere to the course she points out, and do not twist her language to support our own preconceived notions. The power of gravitation, by which a stone is brought to the earth, retains the planets in their orbits; and the principle of electricity which, when excited in a piece of glass or of wax, only enables it to attract a pith-ball or the fibres of a feather, produces, when collected in the sky, all the terrifying effects of a thunder-storm. There surely can be no good reason why we should not investigate the circumstances in these two classes of facts, and why, after due investigation, we should not refer them to the same law, though the scale on which we trace its operations be so extremely different. In the same manner, no prejudice should exist against the theories of the geologist, though he should apply those mechanical and chemical principles, which he can trace in the formation of a minute crystal or a stalactite, or in the arrangement of the bottom of a river, to account for the present appearances of the habitable world.
How far this class of philosophers have adhered to, well ascertained principles, in their geological investigations and reasoning, is a different question. All that we mean to claim for them is, that there is no natural presumption against a theory; that their object is legitimate when they endeavour to form one; and that there are not wanting appearances which may render one plausible. Of late years two principal theories have been proposed to account for geological phenomena, which have attracted such interest as to cause a complete oblivion of every previous hypothesis. Though diametrically opposite in many of their principles, each has men of science and ability for its supporters, and each explains a certain class of facts to the satisfaction of its friends. The one which ranges the greatest number of mineralogists and chemists among its adherents, is called, as we have already stated, the Neptunian or Wernerian, from Werner the great mineralogist of Freyberg, who gave it first the form of a theory founded on observation. The other is denominated the Plutonic system, from its employing the agency of subterranean fire, in accounting for actual appearances, or Huttonian, from the name of the late Dr. Hutton, who gave that particular modification of it which is now considered the most consistent and hilosophical; and which Mr. Playfair and ir James Hall have so ably advocated and illustrated. Both these systems, it will easily be perceived, agree in assuming a state of fluidity as necessary to explain the texture of particular fossils, and the general structure of the mineral kingdom; but they start in direct opposition with regard to its cause, and of course give a different account of every subsequent event, the Wernerian attributing that fluidity to solution in water, the Huttonian to igneous fusion. The products of a mass held fluid, by one of those agents, is in many cases so different from those which would be formed by the Other, that the geologist need not despair of being ultimately able to discriminate between them, and to determine what kind of agency has principally been employed. In the mean time we shall state the opinion entertained of the manner in which each is supposed to have operated, by those who make use of it in their respective systems.
The Wernerian supposes that the surface of our globe presented at first a chaotic mass, in which the materials that compose its solid strata were held in solution by water. In that mixed and confused state, certain changes in the relative situation of the principles took place by motions among them, and the particles were thus placed in a condition favorable for the exertion of chemical affinities. The operation of these chemical attractions was to bring the materials on which they acted into the crystalline shape, which would be more or less perfect in proportion to the freedom in which they were formed, or the interruptions to which in their formation they were subject. An aggregated mass of crystals was thus formed, consolidated and precipitated in the same manner as at present the crystals of salts are deposited from their solution in water. This first precipitation from the chaotic fluid constituted the rocks of the primitive class, so called from this inferred priority of formation. In support of the conclusion on which this name is grounded, the nature and position of these rocks are appealed to. They are evidently in a highly crystalline condition, and they are found nearer the centre of the earth than any other strata of the mineral kingdom. From the nature of the mass before this primitive subsidence, neither animals nor vegetables could exist; at least there have been found in these rocks none of their remains. After these precipitates ■ were separated that compose the primitive class, a nucleus was formed on which subsequent depositions might rest; and the waters; from a cause which it may be difficult to explain, seem to have subsided and left a part of the solid aggregate nearly dry. There Is nothing in this theory, however, which requires us to pronounce upon the question of the time which it might take for these crystallisations and subsidences to take place: or bow rapidly or slowly (as we should term it) they might be effected by the Divine Power.
Still in the fluid the materials of the other strata existed, and these, from similar attractions, had their tendencies to precipitation and arrangement. Precipitates, accordingly, were formed, and arranged on the solid mass already existing. These, however, ar^ found to differ considerably from the primitive class, in having a less perfect crystalline structure, and in containing mixtures like mechanical depositions. From these circumstances they are classified apart under the name of the transition series, and their formation is accounted for by supposing, that, as the chaotic fluid was now diminished in depth, its waves would descend still lower, and come into more immediate contact with that part of the earth's crust already consolidated, and by their agitation, might detach portions of it to mix with the materials still in solution, but gradually depositing; and thus might disturb their formation. In addition to this constant wearing action of the waves, those parts that were gradually elevated above the subsiding waters would be exposed to other causes of attraction from the elements.
The waters continued to subside, and new strata began to make their appearance, forming rocks of the secondary class; but as the action of the elements now extended over a greater surface, and the force of the chaotic waves increased, we find greater supplies of mechanical deposits. These rocks, therefore, having been partly composed of the debris, or disintegrated fragments of the two former classes, have less of the crystalline structure, and are arranged more generally in parallel layers, somewhat like successive mechanical deposits from a fluid. They occupy a lower level than the mountain masses, from the detrition of which they appear partly to have been formed, and rest upon the more crystallised strata as their basis. They often exhibit striking characters of their origin and mode of formation, as may be seen in some kinds of sandstone, puddingstone, and breccia.
When the waters had retired so much as to permit the formation of this class of rocks, and had ceased to cover them, the crust of the earth was prepared for supporting animal and vegetable life, and received from the hand of nature famiies of both in abundance. Accordingly, we find
that organic remains, no vestige of wnich can be found in rocks of the primitive class, and which can be but sparingly discovered in the transition series, increase in quantity and variety as we ascend from the old red sandstone, the earliest of the secondary strata.
The earth, however, if now arranged in the form which it at present assumes, was destined to undergo a mighty catastrophe. The waters which had subsided and left the dry land for the support of animals and vegetables, from inscrutable causes, again rose, resumed their former bed, and a seeond time a chaotic fluid invested the crust of the earth. This fluid must have ascended and almost covered the highest mountains, and in the words of Thomson,
■ A ihoreleu ocean tumbled round the globe.' This rise of |the waters, Werner finds necessary to account for the position and structure of the secondary trap formations, so strangely alternating with or. overlying the other secondary strata. This kind of formation he supposes must once have surrounded the earth, and formed almost a continuous crust, enclosing within it the other strata ; but, by the sudden recession of the waters, that crust was broken, and, the greatest portion of it being carried away, there were only left those * shreds and patches' of it that appear in the shape of detached mountains, columnar eminences, or confused masses of tufa. To the same period may be referred the origin of the coal formation; and to the same causes are its arrangements to be attributed. It is evidently and confessedly a substance of vegetable product, and presupposes the existence of a most luxuriant vegetation, before the organic kingdoms were involved in destruction by waters of the ocean.
After this great catastrophe, the waters again retired from off the face of the earth, and left the dry land for the plants and animals which now cover its surface. As they subsided, the exposed parts were acted upon by the influence of the ocean and the elements. Fragments were broken off from the solid rock, the softer portions were separated from those more indurated, successive layers of the surface were rendered friable and worn away. The debris thus formed was washed from the higher to the less elevated ground, from mountainous country and precipitous eminences, to plains and valleys; and being accumulated on the lower levels, and mixed with decayed animal and vegetable substances, composes the different species of alluvial rocks, and all the varieties of fertile soil.
The only other portion of the crust of the earth for which it would be necessary to account, and for which the theory under consideration can afford no explanation on its peculiar principle, are those formed of the products of volcanic fire. This class of rocks is so inconsiderable when compared with the extent of the stratified masses, and apparently so unconnected with them, that any explanation that may be adopted concerning it will not inuch affect a geological hypothesis, calculated to apply to the state of the more universal formations. The foregoing is the general outline of the Wcrncrian system, but 'here is an observation or two still necessary to complete it.