12 



UXIVEESITY OF VIEGIlSriA PUBLICATIONS 



A. Table of partial analyses of granodiovites, quartz-diorites, and granites. 



I. Limits of variation in granodiorites of Western United States as shown in 



analyses publislied by the United States Geological Survey. 

 II. Average composition of granodiorites as indicated in the analyses included in I, 



III. Limits of variation in quartz-mica diorites of western LTnited States as shown 



in analyses published by the United States Geological Survey. 



IV. Average composition of quartz-mica diorites as indicated in the analyses in- 



cluded in III. 

 V. Limits of variation in granites of middle and southern Appalachians as shown 



in analyses published by the State Geological Surveys. 

 VI. Average composition of southern granites as indicated in the analyses in- 

 cluded in V. 



It will be obser^-ed from a study of the table that the differences are 

 slight in the average composition of granodiorites and quartz-diorites, and as 

 Lindgren states-, "it is often difficult in practice to separate the normal 

 quartz-mica diorite from the granodiorite . . . ." 



As is shown in the tables on pages 37 and 38 of tliis paper the average 

 composition of the Southern, Western, and Xew England granites is 

 strikingly similar, there being essentially no difference in tliis type of 

 rock for the three areas, as would be expected. 



CHARACTERISTIC MIXERAL AXD CHEMICAL FEATURES. 



The characteristic mineral and chemical features of the acid plutonic 

 rocks of the southeastern Atlantic states are best discussed in the necessary 

 detail by individual states, and the principal facts afterwards summarized 

 for the region as a whole. 



^This maximum percentage of CaO is contained in one of the Maryland rooks high 

 in epidote. Omitting this and the next highest percentage of CaO, 3.74 per cent., 

 (vhich is likewise an epidote-bearing rook from Maryland, the maximum percentage 

 of CaO shown in the numerous analyses of the southeastern rocks is 2.76 per cent., 

 contained in one of the Virginia rooks. 



-Op. cit., p. 272. Lindgren restricts granodiorite to the following limits: SiO., 

 59-69 per cent.; ALO3. 14-17 per cent.; FeA, 1-5 to 2.25 per cent.; FeO, 1.5 to 

 4.25 per cent.; CaO, 3 to 6.5 per cent.; MgO, 1-2.5 per cent.; K.O, 1-3.75 per cent.; 

 Na-,0, 2.5-4.5 per cent. 



