QUARTZ-BEARING HYPERSTHENE-ANDESINE SYENITE 209 



The rock from New York, represented by analysis III of table on page 

 207, is from Loon Lake, Franklin County, in the Adirondacks. It has 

 been carefully studied and described by Gushing, 23 who compares it with 

 the akerite described anew by Washington from Essex County, Massa- 

 chusetts, and remarks that the two show great similarity, except that the 

 Massachusetts rock lacks hypersthene. Cushing states that the rocks 

 belong to the variety of augite syenite called "akerite" by Brogger and 

 are quartzose augite syenites. They are clearfy the more acid representa- 

 tives of the syenite group. 



Like the analyses of the Massachusetts and New York rocks, the five 

 analyses of the Norway akerites (II, IV- VII, table of analyses, page 207) 

 show a high alkali content, except IV (5.99 per cent), which is consid- 

 erably lower than the other four and in which K,0 -f- Na 2 ranges from 

 8.74 to 10.88 per cent. In the four analyses (III, V, VI, and VII) 

 showing high alkalies the total normal feldspar exceeds 80 per cent in 

 each case. In the Norway rocks normative plagioclase ranges in composi- 

 tion from andesine (IV) through sodic andesine (V and VI) to nearly 

 albite (II and VII). One (II) is extremely and four (IV to VII) are 

 dominantly alkalic, when the alkali-lime ratio is considered. Two (V 

 and VI) are dominantly sodic and three (II, IV, and VII) have soda 

 and potash in nearly equal proportions. Normative quartz is considerable 

 in II and IV, 2.8 and 0.7 respectively in V and VI, and nil in VII. The 

 position of the Norway akerites in the quantitative system, as shown on 

 page 207, differs widely among themselves. 



The Virginia rocks, on the other hand, contain a much lower alkali 

 content and in general higher lime, the two being, with one exception 

 (IV, page 202), in nearly equal proportions, and therefore alkalicalcic. 

 The proportions of soda and potash in these four rocks are nearly equal. 

 The normative feldspar ranges very much lower than in the Norway 

 rocks; the dominant feldspar is a more calcic plagioclase (andesine), and 

 normative quartz is uniformly higher. The mafic minerals are similar 

 in kind for the Virginia and Norway rocks, except that hypersthene is a 

 constant constituent of the Virginia rocks. 



COMPARISON WITH SYENITE (ANDESINE ANORTHOSITE) OF NELSON 

 COUNTY, VIRGINIA 



The rocks of the Amherst-Nelson counties area 24 are igneous in origin 

 and show in their mineral and chemical composition derivation from a 



23 H. P. dishing: Bull. Geol. Soc. Am., vol. 10. 1899, pp. 177-192. 



24 For a detailed description of the geology of this area the reader is referred to Bull. 

 III-A, Virginia Geol. Survey, 1913, by Watson and Taber. 



XVI — Bull. Geol. Soc. Am.. Vol. 27. 1915 



