EXPLANATION OF PLATE 12. 
Photomicrogeaphs. 
Fig. 1. — The garnets are seen centrally blackened by manganese oxide, and are 
set in a matrix of musaic quartz. 
Fig. 2. — Spessartite — light ; manganese-ore — dark. 
Fig. 4. — Pyroxene — light ; manganese-ore — black. 
