the Peridotites in North Carolina. 



61 



ments that molten glass of a character similar to the basic 

 magnesian rocks would dissolve alumina readily, and as this 

 molten mass began to cool corundum and spinel were the first 

 minerals to separate out. According to this, the corundum 

 and spinel would be the first to crystallize or solidify out from 

 the molten mass of the dunite as this began to cool, and this 

 would take place first on the outer border of the mass, because 

 here it would cool first. Convection currents would then tend 

 to bring a new supply of material carrying alumina into this 

 outer zone, and when this zone was reached, crystallization 

 would take place and the alumina would be deposited as 

 corundum. 



This is essentially the idea advanced by Becker"- in a paper 

 on ".Fractional Crystallization of Rocks," and where this 

 process has taken place in dikes and laccolites, a concentration 

 is observed of the earlier and more basic minerals at their 

 outer boundary. 



The more basic the magma the more fluid it is apt to be, and 

 the more tendency there is for this process to take place, as 

 shown by many well known instances which have been 

 described by different geologists. 



Figure 7 represents the author's idea of the appearance of a 

 vertical cross- section of a mass of dunite, that held corundum 



*This Journal, vol. iv, 1897, p. 259. 



