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UNIVERSITY OF VIKGINIA PUBLICATIOXS 



Similar variation in texture and structure is shown as for the other 

 states, and on this basis the three types, massive even-granular, porphyritic, 

 and schistose, are strongly developed. Where typically developed, these 

 are usually quite sharply differentiated, but the massive granular and por- 

 phyritic fades grade into each other, in practically every locality studied. 



Chemical composition. — In chemical composition the three groups of 

 rocks distinguished above show remarkably close agreement, as is indicated 

 in the following analyses : 



Analyses of Georgia granites} 



I. Average of 21 analyses of massive-granular granites. 

 II. Average of 10 analyses of porphyritic granites. 

 III. Average of 12 analyses of granite-gneisses. 



Essentially no difference is shown in the figures in I and II which 

 represent facies of the same rock mass, but the gneisses (III) average 

 higher in silica, and lower in alumina, iron, magnesia, and lime, while the 

 alkalies for the three types are very closely similar. 



Table K assembles the four constituents, silica, lime, and alkalies, of 

 the 9 leading types of granite, in which the relations between KjO and 

 NajO described above are shown. A few analyses of isolated areas of 

 granite, which strictly conform to one or the other of the 9 types listed, 

 have been omitted from the table. High silica, an average of 71.76 per 

 cent., and low lime, an average of 1.57 per cent., are characteristic features 

 in the composition of the Georgia rocks. 



E. Table of partial analyses of Georgia granites. 



'Georgia Geol. Survey, Bull. No. 9-A, 1902, p. 241. 



