22 Journal of the Mitchell Society \_June 



separate or crystallize out, not according to their fusibility but 

 their solubility in the molten magma. The more basic por- 

 tions being, according to the general law of cooling and crystal- 

 lizing magmas, the less soluble would be the first to separate out. 

 These would be the oxides containing no silica; in the present 

 case the chromite, spinel, and corundum. These minerals would 

 solidify or crystallize out where the molten magma first began 

 to cool, which would be at the contact of the mass with the coun- 

 try rock ; convection currents would tend to bring new supplies 

 of material to the outer boundary, which would deposit its 

 chromic oxide as chromite. 



The more fluid a molten mass of rock becomes the more favor- 

 able will be the movements and other conditions in this molten 

 mass to the bringing about of these changes, and it is in these 

 very basic magnesian rocks that we find the best illustrations of 

 the separation and concentration of the more basic minerals. 



This would account for all the irregularities of the chromite 

 deposits — their pockety nature, the shooting off of apophyses 

 from the main masses of the chromite into the peridotite, the 

 widening and pinching of the chromite " lodes," and the ap- 

 parent non-relation or non-connection of one pocket of chromite 

 with another. There has not been sufficient work done in the 

 IsTorth Carolina chrome mines to demonstrate exactly the po- 

 sition and relation, of the chromite deposits to the gneiss or 

 other country rock, and in the description of other chrome 

 mines but little light has been thrown on this point. The chro- 

 mite would be concentrated near the borders of the peridotite in 

 rounded masses, with offshoots penetrating into the peridotite. 

 The lines of contact near the gneiss would be sharp and nearly 

 regular, while with the peridotite the contact would be very 

 irregular. The pockets of chromite found in the midst of a 

 peridotite formation, which at the present time are isolated 

 and have no connection with each other, were at the time of 

 their formation part of the chromite concentrated near the 

 border of the peridotite, but the rapid erosion to which the 

 rocks has been subjected has worn them down to their present 



