DHUNPORE CARIES

Herbert Daniel Gebauer - 06/01/2018

In the course of the Kumaon survey (1815-1821), Captain Herbert (note 1) observed results of dolomitisation processes and noticed another appearance remarkable in this limestone is the aries [sic! qua: caries; decay, crumbling] that seems to attack lumps small of it, changing the outer coat to the colour, grain, and consistence of chalk. This change is the more remarkable in a rock, which like this is of a blue colour, and possessed of considerable hardness. … the limestone is in general impure; when otherwise, it appears to undergo that superficial caries already noticed (HERBERT, J D 1842: [57-58] lxxvii - lxxviii). On the ascent from Boomot [note 2], which is situated on an extensive flat (river terrace) to Dhunpore … a perfect rotten stone. What the nature or cause of this caries is, which so often appears to attack rocks of the greatest solidity, no one has yet explained in a satisfactory manner. The unchanged rock is of blue colour, impalpable in composition, with a conchoidal facture, and in appearance resembling perfectly the most regular limestone. It is, however, a very impure one, being highly charged with argillaceous or siliceous ingredients, or perhaps with both, occasionally it even strikes fire with steel, and approaches the nature of schist. In its passage into the rotten stone it is observed, first to change a little in colour, becoming gradually more tinged with the peculiar mud colour of the latter, which is so far different from the rotten stone of Derbyshire, as to be of a more yellowish than a brownish tinge. The grain is observed gradually to make its appearance, and the rock to be full of joints or cleavages, till at last it is found of a dirty yellow colour, fine grain, very friable, and with a specific gravity of only 0.9. A series of specimens connecting the two extremes has been collected, which shews the progress of the change with great clearness; a rotten stone of bright colour appears to originate in a real argillaceous schist (HERERT, J D 1842: [100] c). LITHOGRAPHY: In the ascent to Dhunpore, quartz rock is the prevailing substance, which passes on the summit of the ridge into a very thin slaty rock of a yellowish colour, exceedingly hard, and composed apparently of quartz with some talc [note 3]. The laminae of this are not above a tenth of an inch in thickness. They separate with greatest clearness, are often bent or curved, are rather brittle, and consequently not obtainable of any size. This type might be called slaty quartz rock, in contra-distinction to schistose quartz rock. It passes into the pure amorphous type; argillaceous schist, then proceeds, variously intermixed with limestone more or less pure. The former occurs here of an intense black colour, similar to that of basanite. It has a schistose structure, but never separates into thin slates, the attempt to obtain such generally producing a conchoidal surface, or at least one more or less uneven. It is moderately hard, of a fine grain, receives good polish, would form a most superior description of writing slate, and is not even inapplicable to the purposes to which basanite is applied. It has a cleavage, or set of natural joints, the surfaces of which present the appearance of a slight iridescence, or pavonine tarnish. This cleavage is most commonly, or at least very often, transverse to the direction of the schistose structure. It is in contact on two sides, with an argillaceous or siliceous limestone, which in its immediate neighbourhood passes into a perfect rotten stone (HERBERT, J D 1842: [99-100] xcix - c). The nearby copper mine at –>Dhobree … is remarkable for furnishing lumps of limestone, apparently changed by a similar process to that which produced the rotten stone, the result in this case being a perfect chalk; such a change in the surface of limestone fragments is common, and has been noticed in the preceding details; but excepting at Dhobree, I have never met such large pieces so perfectly changed to chalk (ERBERT 1842: [100] c). good polish, would form a most superior description of writing slate, and is not even inapplicable to the purposes to which basanite is applied. It has a cleavage, or set of natural joints, the surfaces of which present the appearance of a slight iridescence, or pavonine tarnish. This cleavage is most commonly, or at least very often, transverse to the direction of the schistose structure. It is in contact on two sides, with an argillaceous or siliceous limestone, which in its immediate neighbourhood passes into a perfect rotten stone (HERBERT, J D 1842: [99-100] xcix - c). The nearby copper mine at –>Dhobree … is remarkable for furnishing lumps of limestone, apparently changed by a similar process to that which produced the rotten stone, the result in this case being a perfect chalk; such a change in the surface of limestone fragments is common, and has been noticed in the preceding details; but excepting at Dhobree, I have never met such large pieces so perfectly changed to chalk ( good polish, would form a most superior description of writing slate, and is not even inapplicable to the purposes to which basanite is applied. It has a cleavage, or set of natural joints, the surfaces of which present the appearance of a slight iridescence, or pavonine tarnish. This cleavage is most commonly, or at least very often, transverse to the direction of the schistose structure. It is in contact on two sides, with an argillaceous or siliceous limestone, which in its immediate neighbourhood passes into a perfect rotten stone (HERBERT, J D 1842: [99-100] xcix - c). The nearby copper mine at –>Dhobree … is remarkable for furnishing lumps of limestone, apparently changed by a similar process to that which produced the rotten stone, the result in this case being a perfect chalk; such a change in the surface of limestone fragments is common, and has been noticed in the preceding details; but excepting at Dhobree, I have never met such large pieces so perfectly changed to chalk (ERBERT 1842: [100] c).