pratt.] DISTRIBUTION. 37 
gested by G-enth, 1 but that, they were both formed during the meta- 
morphism of the rocks from which the schists and gneisses have been 
derived. 
SUMMARY OF CORUNDUM OCCURRENCES. 
From the facts presented in the preceding pages, the occurrences 
of corundum are seen to be of much greater variety than was 
formerly supposed. While the large concentrated masses are still 
confined to the basic magnesian rocks, corundum is scattered in small 
amounts through a number of other rocks, and in the aggregate is in 
very large quantity. 
Of the igneous magmas there are t \\ <> I hat are very distinct from each 
other and that can be designated as the lime-magnesia and the alka- 
line series. In the firsl the mineral components of the rock are free 
from alumina, and where there has been alumina in solution in the 
molten magma it has all separated ou1 either as corundum or spinel. 
In the second series, however, it is only the excess of alumina that 
has separated out ;is corundum, by far the larger percentage having 
united with the alkaline oxides to form ,i feldspar. In all the occur- 
rences that have been examined this phenomenon has been constant. 
It is very evidenl that there are magmas thai contain an excess of 
alumina just as there are magmas with an excesss of silica, and it is 
evident that the alumina separates <>ut as corundum in t he same man- 
ner that silica separates as quartz in granitic rocks. 
DISTRIBUTION <>I CORUNDUM. 
Most of the corundum thai has been mined for abrasive purposes 
has been obtained from the eastern pari of the United States, and has 
been found associated with the long bell of basic magnesian rocks 
extending from Massachusetts to Alabama. It is in i he southern por- 
tion of this belt, in North Carolina and Georgia, that these racks have 
their greatest extent, and it. is in this region that the greatest quantity 
of corundum has been found. During the past few years, however, 
North Carolina is the only State that has produced any corundum and 
Massachusetts and New York the only ones that have produced any 
emery. 
While the production of corundum has been limited almost entirely 
to one locality in North Carolina, it is not because this is the only 
known deposit of this mineral in quantity, but because the better 
deposits have not been worked. The emery deposit that has proved 
of the most economic importance, and which has produced practically 
all the emery mined in the United States, is at Chester, Mass. The 
amount of corundum that has been mined during the past year is 
very much less than the amount of emery, although its market value 
1 Am. Philos. Soc, Vol. XIII, 1»73, p. 22. 
