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UNIVEKSITY OF VIRGINIA PUBLICATIONS 



III. Benjamin quarry, Greenwood county, South Carolina. Bull. No. 2, Series IV, 



S. C. Geol. Survey, 1908, p. 251. 



IV. Cold Point, Greenwood county. South Carolina. Bull. No. 2, Series IV, S. C. 



Geol. Survey, 1908, p. 251. ' 

 V. Average 3 analyses, Newberry, Fairfield, and Lancaster counties. South Caro- 

 lina. Bull. No. 2, Series IV, S. C. Geol. Survey, 1908, pp. 250-255. 

 ^^I. Average 2 analyses, Union and Spartanburg counties, South Carolina. 

 Bull. No. 2, Series IV, S. C. Geol. Survey, 1908, pp. 198-200. 

 VII. Average 4 analyses, Anderson, Laurens-Abbeville, Pickens, and Lexington 

 counties, South Carolina. Bull. No. 2, Series IV, S. C. Geol. Survey, 1908, 

 pp. 250-255. 

 VIII. Average 3 analyses, Fairfield, Lexington, and Kershaw counties, South Caro- 

 lina. Bull. No. 2, Series IV, S. C. Geol. Survey, 1908, pp. 250-255. 



The range in silica is less than for Mar3'lancl and North Carolina, from 

 67.33 per cent, to 71.77 per cent., with an average of 69.57 per cent. In 

 the complete analyses, the range in alumina, ferrous and ferric oxides, 

 magnesia, and lime is proportionately small, indicating in general but 

 small differences in the amounts of the dark mineral and plagioclase. The 

 percentage of quartz as calculated is: I, 20.94; II, 30.72; III, 22.68; 

 IV, 25.98; V, 23.88; VI, 24.60; Yll, 19.26; VIII, 30.84; average, 24.86. 



Only one analysis (I) shows the percentage of ISTaoO to be greater than 

 that of KoO. Five (II, V, VI, VII, and VIII) indicate approximately 

 equal percentages of the alkalies, and two (III and IV) show an excess of 

 KjO over NajO of more than 1 per cent. In each case, however, ISTaaO is 

 molecularly greater than KjO. The range in CaO is about that of so-called 

 normal granites. 



Thin sections of the rocks show the presence of the potassie feldspars, 

 orthoclase and microcline, the latter subject to greater variation in amount 

 than the former. Microperthite, quite generally present, indicates that the 

 potassie feldspar contains some soda. Zonal structure in the plagioclase 

 is rare, and from optical measurements the soda-lime feldspar corresponds 

 to oligoclase. 



Computed from the constituents in the table above, the mineral com- 

 position of the feldspars is shown in table J. 



J. Table of fddspar composition of South Carolina granites. 

 (Numbers correspond to table H.) 



Average. 



Orthoclase _- 



Albite 



Anorthite _— 

 Total plagioclase— 

 Total feldspar . 

 AbnAnm ratio. 

 Or — plag. ratio. 



25.0 

 32.4 

 9.4 

 41.8 

 66.84 



1:1.7 



