50 Pratt — Origin of the Corundum associated with 



respect to its origin. That there are several modes of origin 

 of corundum would seem clear from the various ways in which 

 it occurs. Its association with the plutonic and rnetamorphic 

 rocks, such as granites, gneisses and crystalline schists, is well 

 known, as also its occurrence in basic igneous rocks. The 

 corundum, which is the subject of this paper, is that which is 

 found associated with the peridotites; and the accompanying 

 map, fig. 1, shows the distribution of these and of the corun- 

 dum in western North Carolina. 



In the accompanying pages it is purposed to give the reasons 

 why the corundum should be regarded as having been formed 

 at the same time with the dunite, as having been held in solu- 

 tion by the molten mass of the dunite and having crystallized 

 out among the first minerals as the mass began to cool. 



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Fig. 2. Map of the Webster peridotite area. Jackson County, N. C, showing* 

 near its northern extremity a large block of gneiss entirely surrounded by the 

 peridotites. (After Lewis.) 



This theory of the origin of the corundum depends upon 

 the igneous origin of the peridotites and it seems advisable at 

 this point to review the reasons why the peridotites of this 

 region are to be regarded as igneous rocks, and to state new 

 facts bearing on this view. Most of the points brought out by 

 Lewis have been verified by the author from personal observa- 

 tion, and a brief summary of them is given here : 



The blunt lenticular form in which we find these peridotites 



