OKiGlN IN IGNEOUS ROCKS, 81 
A massive, coarsely to finely granular spinel is found at the Corun- 
dum Hill mine, Macon County, N. C, having- disseminated through 
it small grains and fragments of pink and white corundum. The 
spinel and the corundum are closely associated with chlorite, which 
is here more generally developed between the corundum and the spinel 
and in the spinel (between the granules) than it was at the Carter 
mine. The spinel in the mass appears black, but in small splinters it 
shoAvs a green color. 
The corundum is found m the peridotite in two different relations, 
one in the zone of alteration products developed at the contact of the 
peridotite and the gneiss, and the other in a similar zone of altera- 
tion products, bounded on both sides by the peridotite. 
The line of contact between the zone of alteration products and 
the gneiss was very sharp and distinct in all the border veins exam- 
ined. The minerals developed betw^een the corundum-bearing zone 
and the peridotite are of great abundance and different from those 
between this zone and the gneiss. In the veins that are entirely 
within the mass of the peridotite, the zones of alteration products 
are the same on each side of the seam of corundum and similar to 
those on the peridotite side of a border vein. These phenomena are 
described and illustrated on pages 28-33. 
The appearance and character of the veins vary according as they 
are border veins or interior veins. In an interior vein the approxi- 
mate trend of the vein is toward the center of the mass of peridotite. 
As these veins penetrate the mass they usually grow less and less in 
width until they pinch out. This is especially a prominent feature 
at Buck Creek, Clay County, N. C, and at Laurel Creek, Rabun 
County, Ga. 
In a border vein, however, the corundum seems to extend down- 
ward indefinitely along the line of contact. Supplementary veins 
are often encountered branching off from a border vein toward the 
center of the peridotite, and these, like the true interior veins, grow 
less and less in width until they pinch out entirely. This variation 
in the occurrence of the corundum m the difl'erent veins has been 
observed by many of those who have prospected for and mined corun- 
dum in this region. 
thp:ory of origin in peridotite. 
The theory advanced in this paper is that the corundum was held 
in solution in the molten mass of the peridotite when it Avas intruded 
into the country rock and that it sei)a rated out among the first min- 
erals as the mass began to cool. 
The peridotite magma hokling in sohition the chemical elements 
of the different minerals would be like a saturated liquid, and as it 
Bull. 2(39— U() M 6 
