378 FREDERIC II. LAIIEE 



regular curving edges evidently due to magmatic corrosion and not 

 to subsequent localized granulation or recrystallization. 



9. Some feldspar phenocrysts have zonal structure parallel to 

 the outlines of the corrosion inserts of the groundmass (Fig. 10). 



10. Both quartz and feldspar phenocrysts, and even those 

 feldspar crystals which have zonal structure, are quite free from 

 the type of inclusion of the groundmass which is so common in 

 many metacrysts. 



n. Although two or three feldspar crystals are sometimes 

 attached as if they had grown so (Fig. 16), quartz and feldspar 

 never occur thus together. If the materials of 

 the schist were derived from the breaking up 

 of a granitoid rock, small pebbles composed of 

 both quartz and feldspar would be expected. 

 „ 12. All, or nearly all, of the feldspar pheno- 



FlG. it). — Two J ' . 



attached plagioclase crysts are albite. A clastic rock would be likely 

 individuals which to contain several species of fragmental feldspar. 



occur as a phono- ^ there ^ plenty Q f roc ^ s J n ^g reg i n which 

 crvst. Enlarged 7 * . , 



diameters. nave orthoclase. nucroclme, microperthite, micro- 



pegmatite, etc., among their constituents. 



13. The abundance of albite in this rock suggests that the 

 content of Na may be abnormally high for an argillitic sediment. 

 However, I have not analyzed the rock chemically, and the Rosiwal 

 method would be unsatisfactory on account of the difficulty of 

 determining the particles of the groundmass. 



14. The preponderance of easily recognized pebbles of felsitic 

 rocks in the "egg conglomerate" proves that acidic effusive rocks 

 may be expected in the region. 



If, then, we grant that the quartz-plagioclase porphyry schist 

 is effusive, its composition places it in the class of quartz kera- 

 tophyres. and the similar quartzless rock oi Mormon Hill belongs 

 to the keratophyres. 



Parker Hill white schist. — This is taken as representative of the 

 '•tuff-like schists*' of the Lyman group. It is undoubtedly a 

 metamorphosed clastic as is demonstrated by the following facts: 



1. Megascopically and microscopically it has a distinctly frag- 

 mental aspect. 



