298 Pratt — Corundum in North Carolina. 



of them are cutting irregularly through them. Where these 

 dikes are parallel to the bedding of the schists, the laminated 

 structure of the latter is more apparent. The general strike of 

 these crystalline rocks is N.E.-S.W. and with a dip of about 

 30° to the KW. 



Portions, or bands, of these schists are corundum-bearing, 

 but they are irregularly defined and gradually merge into the 

 normal rock. They have a similar relation to the normal 

 schists that the garnet-bearing bands of a gneiss have to the 

 normal gneiss in which they occur. They are not veins in any 

 sense of the word, but are simply portions of the same mass of 

 crystalline rocks in which corundum occurs as a constituent of 

 the rock. These bands vary in width from a foot or two to 

 12 or 15 feet, but in these wider ones the corundum-bearing 

 portion is not continuous but is intercepted by streaks of 

 barren rock and granitic dikes. 



These bands can be traced for a distance of five or six miles 

 in a N.E.-S.W. direction, sometimes outcropping continuously 

 for nearly a mile. There are at least two of these corundum- 

 bearing bands which are parallel to each other and about two 

 miles apart. The only variation that has been observed. in 

 them is the percentage of corundum and garnet, otherwise 

 they are identical. The percentage of corundum is never high, 

 and from determinations made on samples from various parts 

 of the deposits, it varies from two to five per cent. 



The corundum occurs for the most part in small particles 

 and fragments that have no definite shape and are of a gray, 

 white, and bluish-white color to almost colorless. It is also in 

 crystals from minute ones to some that were observed two and 

 a, half inches long and about one-half an inch in diameter, 

 which are usually fairly well developed in the prismatic zone. 



It is probable that these schists are the result of the meta- 

 morphism of sandstones and shales formed from alluvial 

 deposits of many thousand feet in thickness, that were for- 

 merly the bed of the ocean. By lateral compression these 

 have been folded and raised into the mountain ranges of this 

 section. That these were much higher than at the present 

 time is very evident from the granitic dikes that are of deep- 

 seated origin. By decomposition and erosion the mountains 

 have been worn down to their present condition, thus exposing 

 the schists in contact with granitic dikes which have aided in 

 their thorough metamorphism. The shales were rich in alumina 

 which not improbably was in the form of bauxite, and during 

 their metamorphism the excess of the alumina crystallized out 

 as corundum. This mineral has crystallized out along the 

 planes of lamination so that during the subsequent weathering 

 of the rock the corundum has been left in knotty nodules, 

 studding the surface of the rock, giving it the appearance of 

 containing a high percentage. 



