558 Notices of Memoirs — Dr. W, Mackie — Manganese Dioxide. 



isroTiciHis oip nvcEivnonas, ietc. 

 T. — The Conditions undee which Manganese Dioxide has been 



DEPOSITED IN SEDIMENTARY EoCKS, AS ILLUSTRATED BT THE 



Elgin Sandstones. By William Mackie, M.A., M.D.^ 



MANGANESE dioxide has been observed to occur in the Elgin 

 Sandstones under the following conditions : — (1) In ovoid 

 or rounded spots, from ^ inch to 6 inches in diameter, known to 

 the quarrymen as ' vegetations,' at Newton Quarry, in U.O.R. rocks. 

 From analyses Mn O2 varies from -18 per cent, to "262 per cent. 

 (2) In small nodules, about |- inch in diameter, in Triassic rocks, 

 south-eastofCuttishillock,Mn 02=12-87 percent. (3) Inpunctiform 

 spots around decomposing felspars in sandstone of the Eosebrae 

 division, U.O.E. sandstones = -0715 per cent, of Mn Oj. (4) In 

 small spots or lining minute cavities, and evidently following 

 carbonate of lime in Triassic rocks, at Spynie and Lossiemouth, 

 MnOa = '035 per cent. (5) In veins or lining joints, occasionally 

 parallel to and some distance back from the joint-plane. An 

 example from Bishopmill, U.O.E. , gave Mn O2 1"27 per cent, -f Mn 

 "27 per cent. (6) Along the upper surface, and occasionally 

 irregularly diffused through the interbedded clayey bands of the 

 Eosebrae division. (7) Uniformly diffused through the sandstone in 

 the same way as the much more frequently occurring ferric hydroxide ; 

 «een at Newton, Millstone, and Cloves quarries in the U.O.E. 

 (8) In some organic remains in the same formation ; a scute of 

 Jiothriolepis major gave Mn 2-33 per cent., of Psammosteus Taylori 

 "83 per cent. (9) As a brown or blackish staining on the casts of 

 organic remains. (10) As illustrative examples are cited fragments 

 of cherty limestone in the local Boulder-clays, with their interstices 

 ■filled with Mn Og, the carbonate of lime having been totally removed, 

 and a specimen of ' black ' sand from under Boulder-clay on the 

 Banffshire coast, MnOj 6-58 per cent, -f MnO 48 per cent. 



Experiments made by allowing a dilute solution of manganese 

 sulphate — thirty grains to the gallon — to drip slowly on various 

 rocks and sandstones showed that common chalk and sandstone 

 containing carbonate of lime were darkened in colour within twelve 

 hours. Sandstones without carbonate of lime were not darkened. 

 If the specimens were first moistened with dilute ammonia, caustic 

 soda or potash, or the carbonated alkalies, darkening to a degree, 

 took place very rapidly. Free ammonia was found to exist in every 

 specimen of sandstone from the area examined, and to be particularly 

 plentiful in Newton sandstone. An acid reaction was obtained in 

 some of the ' black ' spots at Newton, due, it was believed, to the 

 oxidation of sulphur, which was also present. Others gave a marked 

 alkaline reaction. The presence of ammonium chloride was also 

 demonstrated in a number of the sandstone specimens. In the 

 presence of ammonia and ammonium chloride, manganese is only 

 precipitated after it is peroxidized, but peroxidization is rapidly 

 effected in the presence of free ammonia or other free alkali. 

 ^ Eead before the British Association, Belfast, Sept. 1902, in Section C (Geology). 



