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The Forest of Dean by H. G. Nicholls

Of these the Coleford High Delf


Hydrates of Iron 57.5 per cent. "Brush" Ore 64.5 ,, Red Calcareous Ore 9.7 per cent. "Blake Ore" 22 ,,

The inhabitants of the Forest consider the ores obtained on the east side superior to those on the west. They likewise suppose, but probably without foundation, that the ore will be found to deteriorate in proportion as the workings descend. Red and yellow ochre of superior quality occur in the iron veins, and have at various times been in considerable request. They are now used in the neighbourhood for marking sheep, and tinting whitewash.

Reverting to the limestone beds of the district, the lower veins are locally called "blue stone," the middle "red stone," and the top vein the "white head," which is largely used as a flux in the smelting furnaces. The researches of Mr. R. Gibbs, of Mitcheldean, have enabled him to furnish me with the following list of fossils discovered by himself in the Forest limestone formation:--

_Zoophyta_ Syringopora reticulata, Turbinolia fungites, Lithostrotion irregulare. _Echinodermata_ Actinoerinus aculeatus, et ,, laevissimus, Platyerinus laevis et ,, rugosus. ,, Poteriocrinus

crassus, et pentagonus. Rhodocrinus costatus, et granulatus. _Mollusca Dimyaria_. Pallastra complanata. _Brachiopoda_. _Terebratula_ hastata. ,, Spirifer glaber, et rhomboideus. ,, Chonetes cornoides, et papilionacea. ,, _Leptoena_ analoga. ,, _Productus_ cora, et longispinus, et martini, et pustulosus et cornoides. _Lamellibranchiata_. Monomyaria. Aviculopecten fallax. Dimyaria. Psammobia complanata.

Pisces.

Ctenacanthus tenuistriatus. Cladodus conicus. Psammodus porosus, et rugosus.

[Picture: Vertical section of the Plump Hill]

The millstone grit beds immediately succeed those of the carboniferous limestone just described, forming a similar belt round the Forest, and disappearing with it on the Blakeney side of the basin. Its chief interest consists in the circumstance that it has been employed from very early times as a material for building; for though it contains a vein of iron ore, little has been done in mining it. Most of the old buildings adjoining the parts where this grit crops out are formed of it, as several of the ancient neighbouring churches show, and likewise the oldest lodges in the Forest; now, however, this kind of stone is seldom used except for boundary walls, and such kind of rough work.

The rest of the outer circle of high land, on whose summit the observer has been supposed to be standing, and which so definitely marks the Forest coal-field, comprises the _lower_ coal measures, containing the lower and upper Trenchard veins, the Coleford High Delf, with the Whittington and Nag's Head seams, which together give about eleven feet of coal. Of these the Coleford High Delf, averaging a thickness of upwards of five feet, and extending over an area of 16,000 acres, is undoubtedly the chief, although in some places it has suffered from various disturbances, the principal of which occur in the neighbourhood of Coleford, extending in a line from Worcester Lodge to Berry Hill, and is marked on the surface by a succession of pools, named Howler's Well, Leech Pool, Crabtree Pool, Hooper's Pool, and Hall's Pool. Mr. Buddle describes the width as varying from 170 to 340 yards in the most defined part, called by the colliers the "Horse," and the dislocations adjoining, the "Lows." "It is not," he remarks, "what geologists term a _fault_, as there is no accompanying dislocation of the adjoining strata. In its underground character it is similar to those _washes_ or aqueous deposits in many coal districts, but it differs from them in not being under the bed of any river, nor in the bottom of a valley, nor does it show itself at the surface." And he adds, "On considering the various phaenomena presented by this fault, and the seam of coal on each side of it, we may infer that it occupies the site of a lake which existed at the period of the deposition of the High Delf seam, and that the carbonaceous matter which formed the seam was accumulated while the water was deep and tranquil. On the water being discharged from the lake, the 'Horse' itself occupied the bed of the river, by which the complete drainage of the lake was effected, and which washed the coal entirely out."


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