INTERMEDIATE CHARACTER OF APPALACHIAN GRANITES 



29 



The above characteristic features of composition, namely, high SiOj 

 and low CaO ; acid oligoclase ; an orthoclase-plagioclase ratio, in most 

 cases, of 1 to less than 2 ; and a computed orthoclase content usually greater 

 than 20 per cent, and considerably less than 40 per cent.^, grovip these 

 rocks in the old system of classification as quartz monzonites. The few 

 exceptions are noted under the discussion of individual states. It is a 

 noteworthy fact that on the basis of orthoclase content (40 per cent, or 

 more on an assumed basis of 60 per cent, total feldspar) there is not a 

 rock represented in the numerous analyses of the entire region that prop- 

 erly would be called granite. 



In the quantitative classification of igneous rocks, the rocks represented 

 b}' the analyses above fall in Class I, persalane (two, Maryland 1, and 

 North Carolina 1, Class II dosalane) ; in orders 3, columbare, and 4, brit- 

 tanare, predominantly the latter, with one in order 1, victorare. Four fall 

 in rang 1, peralkalic; 29 in rang 2, domalkalic; and 5 in rang 3, alkali- 

 calcic ; 29 in subrang 3, sodi-potassic, 7 in subrang 4, dosodic, and 2 between 

 subrangs 3 and 4. They are dominantly domalkalic and sodipotassic. It 

 is interesting to note that not one of the rocks is perpotassic or dopotassic. 



The rocks correspond to the subrang names toscanose (21), lassenose 

 (3), liparose (2), alaskose (2), one each of tehamose, alsbachose, riesenose, 

 amiatose, yellowstonose, dacose, and tonalose, and one each between tosca- 

 nose and lassenose, amiatose and yellowstonose. 



GRANITES OP NEW ENGLAND. 



Twent,y-one analyses- of granites from New England, Massachusetts 

 (6), Maine (6), Vermont (3), New Hampshire (1), Ehode Island (3), 

 and Connecticut (2), show the following limits of variation and average in 

 silica, lime, soda, and potash : 



Granites of New England. 



'Lindgren, W. Op. cit., p. 279. 



-Selected from publications of State and Federal Geological Surveys. 



