601 



that the specimen I have examined is a new variety. But it 

 is also pecuhar in other respects. 1. It contains oxide of 

 copper in appreciable quantity, a substance not occurring in 

 the other psilomelanes, though it was found by Professor 

 Davy, of the Dublin Society, to the amount of 4.5 per cent, 

 in a Swedish ore of manganese, which he considered to be a 

 braunite (see Journal of Geol. Society of Dublin, vol. i. 

 part 3.) 2, The amount of barytes included by it is but 

 about one-third of that found in the ores examined by Ber- 

 thier and Turner. 



As respects the manner of the existence of the barytes 

 always found in psilomelane, and in small quantity in some 

 of the other ores of manganese also ; I may observe that it 

 is the opinion of some high authorities in science, of M. 

 Beudant, for instance, that it and the dentoxide are chemi- 

 cally united, the latter performing the function of an acid. 

 If this idea be correct, it will follow that they are capable of 

 combining in at least two widely different proportions, for 

 the psilomelanes of Berthier and Turner will, upon this 

 view, be represented by the formula 2 BoO, 3 MnaOa, and 

 that which I have analysed by the formula Bo O, 6 Mug O3, so 

 that the latter contains, combined with the same quantity of 

 barytes, four times as much sesquioxide of manganese as the 

 former. 



This Cork psilomelane is obviously a rich ore of manga- 

 nese, though of course inferior to the purer forms of pyro- 

 lusite. It exists in quantity in the district which I have 

 mentioned, and some cargoes of it have been brought into 

 the Dublin market, but have, I am told, been objected to 

 by the manufacturers of the bleaching salt of lime, in conse- 

 quence of its excessive hardness, and the consequent diffi- 

 culty of reducing it to a fine powder. 



About three years ago, I received from Captain Kitto, a 

 Cornish miner, long resident in the south of Cork, an ore of 

 manganese, which appeared so different from those with 



