INTEBJEEDIATE CHARACTER OF APPALACHIAN GRANITES 25 



I. Stone Mountain, DeKalb countv, Georgia. Bull. 9-A, Ga. Geol. Survey, 1902, 

 p. 241. 

 II. Average 9 analj'ses of Oglesb.v dark blue-gray granite, Elbert and Oglethorpe 

 counties, Georgia. Bull. 9-A, Ga. Geol. Survey, 1902, p. 241. 



III. Average 2 analyses of Elberton-Eehols Mill light gray granite. Elbert and 



Oglethorpe counties, Georgia. Bull. 9-A, Ga. Geol. Survey, 1902, pp. 241-242 



IV. Greenville Granite Cos. quarry, Meriwether county, Georgia. Bull. 9-A, Ga, 



Geol. Survey, 1902, p. 241. 

 V. Average 3 analyses of medium grav granite. Campbell and Coweta bounties 

 Georgia. Bull. 9-A, Ga. Geol. Survey, 1902, pp. 241-242. 

 VI. Average 10 analj-ses of porphyritic granites from the Georgia Piedmont re 

 gion. Bull. 9-A, Ga. Geol. Survey, 1902, p. 242. 

 VII. Odessa quarrv, Meriwether county, Georgia. Bull. 9-A, Ga. Geol. Survey 

 1902, p. 242'. 

 VIII. Average 5 analyses of contorted granite-gneiss from the Lithonia, Georgia 

 area. Bull. 9-A, Ga. Geol. Survey, 1902, p. 243. 

 IX. Average 3 analyses of foliated granite, Coweta, Heard, and Meriwether coun 

 ties, Georgia." Bull. 9-A, Ga. Geol. Survey, 1902, p. 243. 



The KjO and ISTajO approximate nearly equal percentages in a majority 

 of the analyses. Of 23 analyses of massive granular rocks, 13 show a slight 

 excess percentage of K^O over NajO, the excess of KjO ranging from 0.16 

 to 1.20 per cent., with an average for the 13 of 0.638 per cent, excess of 

 KjO. Six of the 10 analyses of the porphyritic rocks show a small excess 

 percentage of KjO over ISTajO, ranging from 0.11 to 1.43 per cent, with an 

 average of 0.845 per cent, excess of KjO. Eight of the 12 analyses of the 

 granite-gneisses show a slight excess percentage of KjO over jSTa^O, ranging 

 from 0.11 to 1.92 per cent., with an average of 0.766 per cent, excess of 

 KjO. With only one exception, a granite-gneiss from Srellville, Gwinnett 

 county, ISTajO molecularly exceeds KgO in each of the 45 analyses. 



The high soda content in these rocks is derived principally from the 

 prevailing large amounts of plagioclase (oligoclase) ; from the replacement 

 of a part of the KjO by NajO in the potassie feldspar; and from micro- 

 perthite, which is quite generally present though variable in amount. 

 Optical measurements of the plagioclase individuals indicate an acid oligo- 

 clase. Albite occurs as intergrowths with a part of the potassie feldspar. 

 Zonal structure is sometimes developed in the feldspars, but the variation 

 in extinction between the center and periphery is not great. 



The mineral composition of the feldspars as calculated from the data 

 in table K, is indicated in table M. 



