c Report of the Mineralogical Survey [No. 126*. 



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. 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 

 fracture, 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. 



222. The rock in the neighbourhood of Dhunpore is, as I have 

 already stated, a quartz rock, it is distinguished for its peculiar shatter- 

 ed and fissured aspect, no trace of stratification being observable except 

 on the great scale. The irregularity of the strata is great, and the 

 change of dip frequent. A mass of red dolomite appears in the middle 

 of it east of the village, and it is in this latter rock that the copper 

 mines are situated. This dolomite is evidently connected with the 

 siliceous limestone on the Dhobree side, in which also a mine is worked, 

 but the produce is inconsiderable. This mine is remarkable, however, 

 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 frag- 

 ments 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. These fragments are used as a flux in the reduction 

 of the copper ores. 



