C. E. De Ranee — Mineral Veins in the North-west Country. 307 



In some of the nodules, cracks radiating from the centre have been 

 filled with galena and iron pyrites ; those metals would appear to 

 have been introduced in a soluble state after the formation of the 

 cracks. 



In the adjoining district of Weardale, in Durham, Spathic iron 

 ores occur, in a similar manner, in lodes associated with lead and zinc 

 ores traversing the Mountain Limestone ; the higher part of these 

 lodes are often found to be changed into brown haematite by the 

 oxidation effected by air, and the percolation of water from above, 

 which transmutation is found to descend for a considerable distance 

 in the Spathic lodes of the Middle Devonian of North Devon and 

 Somerset, described by Mr. Hilary Bauerman ; ^ and similarly large 

 crystals from Hiittenberg, in Carinthia, in the Museum of Practical 

 G-eology, exhibit the same change from " th« elimination of car- 

 bonic acid, and the absorption of oxygen and water," ^ — a like change 

 having superficially converted crystals of iron pyrites "into brown 

 iron ore, by the elimination of sulphur and the addition of oxygen 

 and water." ^ 



By a similar process, sulphide of lead and blende, exposed to the 

 influence of waters charged with bicarbonate of lime, becomes super- 

 ficially converted into carbonates, which is the case with lead left in 

 several levels driven at the commencement of the present century 

 in Tynehead, especially in the higher levels, water gradually losing 

 its power of assisting the change from carbonate of iron to brown 

 oxide, and of sulphide of lead and blende to carbonate, in proportion 

 to the depth traversed, the oxygen probably having been taken up 

 by the proto-oxides of iron in the shale, as suggested by Prof. Eogers, 

 and Mr. Wallace, in his work on the Veins of Alston Moor. 



In that work he describes the large quantities of carbonic acid often 

 found in levels driven through shale in that country, and particularly 

 the difficulty of contending with it at Long Clough Mine, Nenthead, 

 where in making "a rise" to the surface, from the level, a seam of 

 water charged with carbonic acid gas was met, which, when bored 

 into from above, ran down the rise with a constant flow of water 

 and gas. Mr. Wallace throws out the suggestion that the latter may 

 be derived from the decomposition of overlying peat, but as it so 

 often fills the cavern connected with the " flats " of the Great Lime- 

 stone, and as I found it to occur suddenly in the main adit level of 

 the Whitewell Mine in Yorkshire, through which there is perfect 

 ventilation, it would appear to be more probable, that it is due to 

 chemical change going on in the adjacent rocks, possibly the action 

 of sour peat waters in limestone. 



Many of the caverns in which occur the " flats " of this district 

 appear to have been eaten out by the action of acidulated waters, 

 acting along lines of joints unconnected with faults, rather than 

 by a run of water, it being only certain beds, as the Great, Scar and 

 Tyne-bottom Limestones that readily decompose, and form these 



1 Metallurgy of Iron, third edition, 1872, p. 80. 



2 Hunt and Rudler, Descriptive Guide to the Museum of Practical Geology, Third 

 edition, p. 84. ^ Op. cit., p. 94. 



