60 Pratt — Origin of the Corundum associated with 



actinolite and some green chlorite ; 4 and 8, a grayish, rather 

 fibrous, enstatite rock that merges into 3 and 9 ; 5 and 7, green 

 chlorite passing into 6, a mass of chlorite, corundum and 

 spinel. 



Although the section just described represents a particular 

 one, it was observed that in all of the dunite veins, the charac- 

 ter of the vein was the same on each side of the corundum- 

 bearing zone. As has been stated already, either a talcose or 

 serpentine rock may be the limit of the cross section. In one 

 of the dunite veins at Corundum Hill, near the west end of 

 the outcrop, the zone of corundum, chlorite and vermiculites 

 is in direct contact with a serpentine rock both on the hanging 

 and foot wall. This zone is divided, and in one place almost 

 pinched out by a mass of serpentine rock. 



The appearance and character of the veins vary according as 

 they are contact-veins or dunite-veins. In a dunite-vein the 

 approximate trend of the vein is towards the center of the 

 mass of dunite. As these veins penetrate the dunite 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 contact-vein, however, the corundum seems to extend 

 downward indefinitely along the line of contact. Supple- 

 mentary-veins are often encountered branching off from a 

 contact-vein, toward the center of the dunite, and these, like 

 the true dunite-veins, grow less and less in width until they 

 pinch out entirely. This variation in the occurrence of the 

 corundum in the different veins has been observed by many of 

 those who have prospected for and mined corundum in this 

 region. 



Discussion of the Problem. — The theory advanced by the 

 author, as given in the introduction, is that the corundum was 

 held in solution in the molten mass of the dunite when it was 

 intruded into the country rock and that it separated out among 

 the first minerals, as the mass began to cool. 



The dunite magma holding in solution the chemical elements 

 of the different minerals would be like a saturated liquid and 

 as it began to cool the minerals would crystallize out, not 

 according to their infusibility but according to their solubility 

 in the molten magma. The more basic portions, according to 

 the general law of cooling and crystallizing magmas, being the 

 most insoluble, would therefore be the first to separate out. 

 These would be the oxides containing no silica, which in the 

 present case would be alumina and chrome spinel and the 

 corundum. 



Morozewicz* has shown by some very important experi- 



* Zeitschr. fur Kryst., vol. xxiv, p. 281, 1895. 



