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been inaccessible. Had the strata of Coal, been continu

many deep and rich mines would have (See Pl. 65. Fig. 3. and Pl. 66. Fig. 2.) Shale and Grit, that alternate with the ously united without fracture, the quantity of water that would have penetrated from the surrounding country, into any considerable excavations that might be made in the porous grit beds, would have overcome all power of machinery that could profitably be applied to the drainage of a mine; whereas by the simple arrangement of a system of Faults, the water is admitted only in such quantities as are within control. Thus the component strata of a Coal field are divided into insulated masses, or sheets of rock, of irregular form and area, not one of which is continuous in the same plane over any very large district; but each is usually separated from its next adjacent mass, by a dam of clay, impenetrable to water, and filling the fissure produced by the fracture which caused the Fault. (See Pl. 66. Fig. 2. and Pl. 1. Figs. 1,—l, 7.)

If we suppose a thick sheet of Ice to be broken into fragments of irregular area, and these fragments again united, after receiving a slight degree of irregular inclination to the plane of the original sheet, the reunited fragments of ice will represent the appearance of the component portions of the broken masses, or sheets of Coal measures we are describing. The intervening portions of more recent Ice, by which they are held together, represent the clay and rubbish that fill the Faults, and form the partition walls that insulate these adjacent portions of strata, which were originally formed, like the sheet of Ice, in one continuous plane. Thus each sheet or inclined table of Coal measures, is enclosed by a system of more or less vertical walls of

very few instances ascertained; they are accompanied by a subsidence of the strata on one side of their line, or (which amounts to the same thing) an elevation of them on the other; so that it appears, that the same force which has rent the rocks thus asunder, has caused one side of the fractured mass to rise, or the other to sink. The fissures are usually filled by clay." Geology of England and Wales, Part I. p. 348.

broken clay, derived from its argillaceous shale beds, at the moment in which the Fracture and Dislocation took place; and hence have resulted those joints and separations, which, though they occasionally interrupt at inconvenient positions, and cut off suddenly the progress of the collier, and often shatter those portions of the strata that are in immediate contact with them, yet are in the main his greatest safeguard, and are indeed essential to his operations.*

The same Faults also, while they prevent the Water from flowing in excessive quantities in situations where it would be detrimental, are at the same time of the greatest service, in converting it to purposes of utility, by creating on the surface a series of Springs along the line of Fault, which often give notice of the Fracture that has taken place beneath. This important effect of Faults on the hydraulic machinery of the globe extends through the stratified rocks of every formation. (See Pl. 69. Fig. 2.) It is also pro

"If a field of coal (says Mr. Buddle) abounding in water, was not intersected with slip Dikes, the working of it might be impracticable, as the whole body of water which it might contain would flow uninterruptedly into any opening which might be made into it; these Faults operate as Coffer Dams, and separate the field of coal into districts."—Letter from Mr. John Buddle, an eminent Engineer and experienced Coal Viewer at Newcastle, to Prof. Buckland, Nov. 30, 1831.

In working a coal Pit, the Miner studiously avoids coming near a Fault, knowing that if he should penetrate this natural barrier, the Water from the other side will often burst in, and inundate the works he is conducting on the dry side of it.

A shaft was begun about the year 1825, at Gosforth, near Newcastle, on the wet side of the 90 fathom Dike, and was so inundated with water that it was soon found necessary to abandon it. Another shaft was then begun on the dry side of the dike, only a few yards from the former, and in this they descended nearly 200 fathoms without any impediment from water.

Artificial dams are sometimes made in coal mines to perform the office of the natural barriers which Dikes and Faults supply. A dam of this kind was lately made near Manchester, by Mr. Hulton, to cut off water that descended from the upper region of porous strata, which dipped towards his excavations in a lower region of the same strata, the continuity of which was thus artificially interrupted.

bable that most of the Springs, that issue from unstratified rocks, are kept in action through the instrumentality of the Faults by which they are intersected.

A similar interruption of continuity in the masses of Primary rocks, and in the rocks of intermediate age between these and the Coal formation, is found to occur extensively in the working of metallic veins. A vein is often cut off suddenly by a Fault, or fracture, crossing it transversely, and its once continuous portions are thrown to a considerable distance from each other. This line of fracture is usually marked by a wall of clay, formed probably by the abrasion of the rocks whose adjacent portions have been thus dislocated. Such faults are known in the mines of Cornwall by the term flucan, and they often produce a similar advantage to those that traverse the Coal measures, in guarding the miner from inundation, by a series of natural dams traversing the rock in various directions, and intercepting all communication between that mass in which he is conducting his operations, and the adjacent masses on the other side of the flucan or dam.*

It may be added also that the Faults in a Coal field, by interrupting the continuity of the beds of coal, and causing their truncated edges to abut against those of the uninflammable strata of shale or grit, afford a preservative against the ravages of accidental Fire beyond the area of that sheet in which it may take its beginning; but for such

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My object is rather to suggest whether the arrangement of veins, &c. does not argue design and a probable connexion with other phenomena of our Globe.

"Metalliferous veins, and those of quartz, &c. appear to be channels for the circulation of the subterraneous water and vapour; and the innumerable clay veins, or 'flucan courses' (as they are termed in Cornwall,) which intersect them, and are often found contained in them, being generally im. pervious to water, prevent their draining the surface of the higher grounds as they otherwise would, and also facilitate the working of mines to a much greater depth than would be practicable without them."-R. W. Fox on the Mines of Cornwall, Phil. Trans. 1830, p. 404.

a provision, entire Coal fields might be occasionally burnt out and destroyed.

It is impossible to contemplate a disposition of things, so well adapted to afford the materials essential to supply the first wants, and to keep alive the industry of the inhabitants of our earth; and entirely to attribute such a disposition to the blind operation of Fortuitous causes. Although indeed it be dangerous hastily to have recourse to Final causes, yet since in many branches of physical knowledge, (more especially in those which relate to organized matter,) the end of many a contrivance is better understood, than the contrivance itself, it would surely be as unphilosophical to hesitate at the admission of final Causes, when the general tenor and evidence of the phenomena naturally suggest them, as it would be to introduce them gratuitously unsupported by such evidence. We may surely therefore feel ourselves authorized to view, in the Geological arrangements above described, a system of wise and benevolent Contrivances, prospectively subsidiary to the wants and comforts of the future inhabitants of the globe; and extending onwards, from its first Formation, through the subsequent Revolutions and Convulsions that have affected the surface of our Planet.

CHAPTER XXI.

Advantageous Effect of Disturbing Forces in giving Origin to Mineral Veins.*

A FARTHER result attending the Disturbances of the surface of the Earth has been, to produce Rents or Fissures in the Rocks which have been subjected to these violent

VOL. I.

* See Pl. 1. Figs. k 1.—k 24, and Pl. 67. Fig. 3.

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movements, and to convert them into receptacles of metallic ores, accessible by the labours of man. The greater part of metalliferous veins originated in enormous cracks and crevices, penetrating irregularly and obliquely downwards to an unknown depth, and resembling the rents and chasms which are produced by modern Earthquakes. The general disposition of mineral veins within these narrow fissures, will be best understood by reference to our first Section. (Pl. 1. Figs. k 1.-k 24.) The narrow line which pass obliquely from the lower to the upper portion of this Section, represent the manner in which Rocks of various ages are intersected by fissures, which have become the Receptacles of rich Treasures of Metallic Ore. These fissures are more or less filled with various forms of metalliferous and earthy minerals, deposited in successive, and often corresponding layers, on each side of the vein.

Metallic Veins are of most frequent occurrence in rocks of the Primary and Transition series, particularly in those lower portions of stratified rocks which are nearest to unstratified crystalline rocks. They are of rare occurrence in Secondary formations, and still more so in Tertiary

strata.*

* M. Dufrênoy has recently shown that the mines of Hæmatite and Spathic iron in the Eastern Pyrenees, which occur in Limestones of three ages, referable severally to the Transition Series, to the Lias, and to the Chalk, are all situated in parts, where these Limestones are in near contact with the Granite; and he considers that they have all most probably been filled by the sublimation of mineral matter into cavities of the limestones, at, or soon after the time of the Elevation of the Granite of this part of the PyreThe period of this elevation was posterior to the deposite of the Chalk formation, and anterior to that of the Tertiary Strata. These Limestones have all become crystalline where they are in contact with the Granite; and the Iron is in some places mixed with Copper pyrites, and argentiferous galena. (Mémoire sur la Position des Mines de Fer de la Partie orientale des Pyrénées, 1834.)

nees.

According to the recent observations of Mr. C. Darwin, the Granite of the Cordilleras of Chili (near the Uspellata Pass) which forms peaks of a height probably of 14,000 feet, has been fluid in the Tertiary period;

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