THE LYMAN SCHISTS OF NEW HAMPSHIRE 



373 



smaller phenocrysts are thirty or forty times those of the larger 

 groundmass grains and there, is no gradation between the two 



(Fig. 3)- 



Clear, but with a few vacuoles, the quartz phenocrysts display 

 only slight crushing, and this is mostly peripheral (Figs. 4-7). 

 Their corners have been rounded. Several individuals are invaded 

 by long narrow bays of the groundmass (Figs. 5 and 8). It is 

 worth while noting that, although the outer borders of these pheno- 

 crysts are jagged on account of granulation 

 and penetration by mica laths, the edges of 

 the embayments are clean-cut and smoothly 

 curving. 



Fig. s 



Fig. 6 



Fig. 8 



Fig. 5. — Quartz phenocryst with edges serrate on account of marginal granu- 

 lation and penetration by mica laths. Note smooth outline of the embayment (a). 

 Enlarged 26 diameters. 



Fig. 6. — Detail of outer edge of the quartz phenocryst represented in Fig. 5. 

 The shaded area is quartz (Q) . The small laths are mica (M) . 



Fig. 7. — Quartz phenocryst showing terminal granulation at pole of minimum 

 compression (c). a-b is the edge of the thin section. Enlarged 20 diameters. 



Fig. 8. — Part of a large quartz phenocryst. The border zone, a-b, is a granu- 

 lated portion of the phenocryst. Outside this zone is the much finer, uniform ground- 

 mass (not figured). Several embayments of the groundmass are shown, one cut 

 longitudinally (c), and the others intersected transversely at various angles. Note 

 regular outlines of these embayments as compared with the jagged border of the grain 

 as a whole. The figure is drawn from a microphotograph, but not with absolute 

 precision in the finer details. Enlarged 16 diameters. 



Like the quartz, the plagioclase phenocrysts are not severely 

 crushed (Fig. 9) . The angle of extinction on sections approximately 

 perpendicular to the albite twinning varied between 13 and 17 . 

 This and the fact that the index of refraction was always lower than 

 that of balsam indicate that the mineral is albite. Some grains 

 have very good crystal outlines (Fig. 10), but as a rule they have 

 had their corners more or less rounded (Fig. 3). 



