26 JOURNAL OP THE 



idotite belt, which occur t3^pically in blunt lenticular 

 form with a long'er axis of from a few hundred to a 

 thousand feet or more and oriented with the lamina- 

 tion in the surrounding- gneiss. Sometimes they take 

 the form of narrow strips two or three miles in length.* 



Three types of ma.irnesian rocks are found in this 

 belt: namely, jyeridotitcs, pyroxenites, and amphibo- 

 lites, characterized by the predominance of olivine, py- 

 roxene and hornblende respectively. Pyroxenites and 

 amphibolite frequently occur in small masses in close 

 association with peridotites, and sometimes form im- 

 portant independent masses, but probabl}^ more than 

 nine-tenths of the outcrops are peridotites. 



The Peridotites. The accepted classification of 



these rocks is used here merely as a matter of conveni- 

 ence. No such division into distinct classes is possible 

 in the field; and the names here g-iven represent sim- 

 ply mineralog-ic varieties of the same petrog'raphic 

 unit. Occasionally these varieties form separate mass- 

 es, but g-enerally they g-rade insensibly into each other, 

 and sometimes within the limits of a sing-le small outcrop. 

 Dtinite, essentially the pure olivine rock, with acces- 

 sory chromite or picotite, is by far the most important, 

 since it constitutes almost the entire body of a g-reat 

 majority of outcrops. Harzburgite (Saxonite), the 

 olivine-enstatite rock, constitutes larg-e masses in some 

 of the northwestern counties of North Carolina, but it 

 is usually found as a local variety of dunite. "Perid- 

 osteatite" and "g'linkite" seem to be only partially 

 altered forms of this rock, consisting- of large olivine 

 crystals (or serpentine) and talc. Amphibole-ficrite, 



* See map (Plate Ij published in Bull. 11, N. C. Geological Survey, 

 1895. 



