JE. Wethered — Hcematite JDeposifs. 



523 



iron diffused through the rocks." The chemical reactions which 

 take place are briefly these. Iron in the state of ferric oxide comes 

 in contact with decomposing vegetation and yields up oxygen to 

 the carbon, a molecule of carbonic acid being formed by the com- 

 bination of one atom of carbon with two of oxygen. The iron is 

 then reduced to the ferrous state in which it is soluble in water con- 

 taining carbonic acid. Another chemical change then takes place, 

 by which the iron unites with carbonic acid and a carbonate results. 

 When oxidation is possible the carbonate of iron becomes oxidized, 

 and a deposit of peroxide of iron takes place. A practical 

 instance of what I have just described was seen when down the 

 Easton Colliery, near Bristol, a few months since. Water was 

 issuing from some old workings, and on entering a road of the mine 

 where fresh air was travelling, a ferruginous deposit took place. 

 Again, I once had occasion to descend an old shaft of a coal-mine 

 which had not been worked for many years ; near the bottom of 

 the shaft, water was issuing from the old workings, and there was 

 a deposit of peroxide of iron about half an inch deep. On pene- 

 trating further into the workings where the atmosphere had been, 

 until recently, strongly diluted with carbonic acid, there was an 

 entire absence of such a deposit. 



Mr. Etheridge has extensively referred to the hematite deposits in 

 the Carboniferous rocks of the West of England,^ and mentions the 

 occurrence of ore "nearly everywhere" where the Magnesian Con- 

 glomerate rests upon the Carbonifei'ous Limestone, and a section is 

 given which admirably shows the hollows or "pockets " in which it 

 is found. The deposits, however, which occur in the limestone are 

 differently situated compared with those which rest upon the top, to 

 which the term "pocket" is appropriately applied. The following is 

 a section of a portion of the Carth Mine near Cardiff, which shows 

 the position in which the hgematite occurs. 



Section showing mode of Occiirrence of Haematite in the Carboniferous Limestone. 



Carth Mine near Cardiff. 



While visiting this mine, T was much struck with the resem- 

 blance of worked-out so-called " pockets " to natural caverns. Of 



1 Proceedings of the Cotteswold Club, 1865, p. 47. 

 Society, 1870, p. 183, from which quotation is taken. 



Also Quart. Journal of Geol. 



