62 



Pratt — Origin of the Corundum associated with 



in solution, soon after its intrusion into a gneiss. In this figure 

 the corundum zone has been greatly exaggerated in order to 

 better illustrate the cross-section. The corundum would be 

 concentrated toward the borders of the dunite and would make 

 a sharp and nearly regular contact with the gneiss. With the 

 dunite, however, the contact would sometimes be sharp and 

 regular, while at others there would be an irregular line of con- 

 tact and masses of the corundum would penetrate into the 

 dunite. 



The rapid erosion to which the rocks in this mountain region 

 have been subjected would readily wear them down to their 

 present condition, represented by the dotted lines in tig. 7. 



The dunite-veins, I, II, and III in tig. 7, which at the 

 present time have no connection with each other but are each 

 separate and distinct, were at the time of their formation part 

 of the corundum concentrated along the border of the dunite. 

 Some of these veins would soon be worked out, while others 

 might be explored for a hundred feet or more without any 

 apparent change in their width. 





mm 



\ : : ';'. ■•/• : p unite. \%^f}\ Coru7idum.^\ JijjGxeiw. 



in 



the 



This explanation will account for all the variations 

 occurrence of the corundum in the different veins. 



The corundum crystallizing out from the molten dunite, 

 which would be a very basic magma, would be concentrated 

 toward the margins and where in many cases there would be a 

 sharp separation (at the time of formation) between the corun- 



