ORIGIN IN METAMORPHIC ROCKS. 95 
possible variety of calcareous, siliceous, and argillaceous rocks, do 
underlie at this location the rocks exposed id the surface, and these 
would probably be capable of furnishing material that could be the 
source of the sapphires. The parallel dike of nearly similar rock 
which cuts the limestones about 600 feet north of the sai)phire dike 
does not, however, contain any gems, and tliis has been thoroughly 
prospected. It may be that tlie shales of the HeU foruiation underlie 
the limestone and Cambrian rocks in sucli a position as to be cut by 
the sapphire dike and that they st()}:> before reaching a point where 
the parallel dike has been intruded. Such beds of shale would be 
readily shattered by the intrusion of igneous rocks, and poi'tions of 
the shattered shales would naturally be included in the intrusive mass. 
These included fragments of shale would be dissolved by the molten 
magma, its heat being very naturally maintained, as it is in the form 
of an intruded mass. Local areas would be formed in the magma 
that would be very rich in alumina, and as the magma began to cool 
corundum crystals w^ould separate out in these alumina-rich areas. 
Such a formation of the corundum is in accord w^ith the laboratory 
experiments, as described under the artificial production of corundum, 
and the form of the crystals is also in accord Avith that of pyrogenetic 
corundum. 
Mr. W. H. Weed « makes the following statement regarding the 
Igneous origin of these sapphires : 
It is apparent from a study of the sapphires themselves that they crystallize 
out of the rock ; but it is also evident that partial resorption took place before 
final consolidation, since many of the sapphires show deeply corroded surfaces; 
others are rounded masses whose crystalline outline is nearly effaced, while 
many of them are surrounded by a blackish crust. If the molten rock could 
dissolve the sapphires at this stage, it is certain that it could dissolve clay 
shale as well. 
As has been stated, the upper portion of these dikes is thoroughly 
altered and decomposed, so that their original character is obscured, 
and they are now ocherous, clayey bodies. Where the dikes are less 
decomposed they begin to have a brecciated appearance, which is 
undoubtedly due to the fragments of limestone that have been broken 
off during the intrusion of these dikes through the limestone. At 
depths varying from 30 to 50 feet the unaltered rock begins to be 
encountered. 
ORIGIN OF CORUNDUM IN METAMORPHIC ROCKS. 
ORIGIN IN AMPIIIHOLE-SCIIIST. 
The occurrence of corundum in the amphibole-schist of Cow^ee Val- 
ley, Macon County, N. C, has been described in detail on pages 57-59. 
The rock is composed chiefly of labradorite, aniphibole, and garnet, 
« Twentieth Ann. Kept. U. S. Geol. Survey, pt. 3, 1898-99, p. 458. 
