434 PROFESSOR HEDDLE ON 
wad, and have almost a black colour. This diminishes in quantity as the layers 
pass from the centre of the lump, the colour passing to brown. The impregna- 
tion suddenly ceases, when the concentric structure at once disappears. These 
layers, when placed in a weak acid, yield very varying amounts of insoluble 
matter,—apparently wad. 
Here the manganesian mineral seems to have imparted to the calcite its 
own tendency to concentric deposition. 
Wad. 
This was found fillmg small cavities and rifts in white quartz boulders 
which lay in the bed of the “ Dirty Burn,” to the south of Dunoon, Argyllshire. 
These quartz boulders were quite fresh in appearance, and seemed to have 
been swept down from a corry in the Bishop’s Hill. They contained in other 
cavities, chlorite, and pyrite in fine crystals. The ‘“‘ wad” was in a loose, inco- 
herent, powdery state, and of a blue-black colour. It yielded 23:7 per cent. of 
water in the bath. . 
Dissolved in moderately strong acid, it yielded— 
Manganous Oxide. A ; ; 38° 575 
Ferric Oxide, : ‘ : ; : 11-828 
Alumina, . ; ; : ‘ 5 6°317 
Lime, . ; : 5 ; : 2° 784 
Magnesia, . ; ; : ; ; 1:008 
Potash, 1:497 
Soda, . : ; ; : , 1°415 
Water and Oxygen, . : : 13-184 
76 *608 
And insoluble,—which, upon fusion with Fresenius’s flux, yielded 
Silica, . ; c : P F 2 16°532 
Alumina, . ; : 5 +376 
Lime, . : : ; ; ; *903 
Magnesia, . : : ’ : *403 
23-214 
99-822 
Insoluble Silica «812 per cent. 
This seems to be a very impure wad. 
Craigtonite. 
Stains, dendrites, and thin filmy coatings on rocks, are very frequently pro- 
nounced to be “manganese,” or manganesian, if these have a brown, or even a 
