86 CORUNDUM, ITS OCCURRENCE AND DISTRIBUTION. 
The penetration of molten material carrying corundum into the 
gneiss during the differentiation of the molten peridotite would 
explain the occurrence of any corundum found in the gneiss adjoin- 
ing a border vein. There is a similar occurrence of the sulphides 
penetrating into the gneiss during the cooling and differentiation of a 
molten gabbro, which is well illustrated in Vogt's« article and has 
been rei:)roduced by Adams.^ 
SUMMARY. 
This theory of the igneous origin of the corundum associated with 
the peridotites is in accord with the field observations and laboratory 
experiments of Morozewicz ^ and Logorio '^ on the solubility of alu- 
mina in a molten basic glass, and the separating out of the corun- 
dum and spinel as the first minerals when the glass began to cool also 
gives strong support to the igneous theory of the origin of the 
corundum here advanced. 
Thus both the facts observed in the field and those obtained in the 
laboratory point to the same conclusion regarding the origin of the 
corundum associated with the peridotite rocks. 
At Pelham, Mass., and at Bad Creek, Sapphire, N. C, where the 
corundum is found in a zone of biotite between the harzburgite (sax- 
onite) and the gneiss, it is undoubtedly the result of contact meta- 
morphism of the igneous rocks on the gneiss. 
At a number of the corundum veins in these peridotite rocks, feld- 
spar, which is undoubtedly one of the original minerals of the rock 
and not a secondary product, is found associated wdth the corundum. 
There is a marked difference noticed in the associated minerals when 
the feldspar is present; chlorite is not thoroughly developed, and en- 
statite is not so common, Avhile margarite is quite abundant and zoisite 
is not uncommon. These last two minerals are rarely met with at 
tho corundum veins Avhich are free from feldspar. 
The separation of alumina from these peridotite magmas has given 
rise to some interesting problems ' bearing directly upon the occur- 
rence of the associated minerals spinel, chromite, and feldspar in a 
corundum vein. 
At the various peridotite localities in North Carolina and Georgia 
the following phenomena have been observed : 
1. Peridotite rocks containing small particles and grains of chro- 
mite, but no corundum or spinel. 
2. Peridotite rocks containing deposits of chromite (which upon 
« Zeitschr. fur prakt. Geol., Nos. 1, 4, and 7, 1893. 
"Am. Jour. Sci., 4th ser., vol. 4, 1897, p. 422. 
'■ Loc. cit. 
"Zeitschr. fiir Krystall., vol. 24, 1895, p. 285. 
* Pratt, J. H., Am. Jour. Sci., 4th ser., vol. 8, 1898, p. 227. 
