MICROSCOPIC DESCRIPTIOK 435 



H. Calciferous epidotic hornblende schist, West One hundred and thirty-fifth 

 street, near Eleventh avenue. 



I. Quartz-diorite schist, West Two hundred and seventh street and Prescott 

 avenue. 



J. Epidotic diorite schist, One hundredth street and Fifth avenue. 



In the thin-sections (plate 62) hornblende scales largely predominate, 

 with more or less hematite and zoisite included or around their margins, 

 and are separated by little patches of a limpidly clear and colorless mosaic 

 of feldspars and quartz. As accessories, biotite, magnetite, zircon, and 

 pyrite also occur. The paragenetic relationship appears to be as follows : 



Zircon (rare), biotite, hematite, zoisite, hornblende, magnetite, feld- 

 spars, quartz, pyrite (and sometimes epidote and calcite). Nearly all 

 of these grains or plates lie in parallel position, so marking the foliation 

 plane, and with their longer axes parallel, so marking the fibration 

 texture of the schist. 



Hornblende occurs in short, brownish, and bluish green blades and 

 largely in broad scales and shreds of very irregular forms, sometimes 

 perforated with rounded holes (see figure 1, plate 62) ; average length, 

 0.4 to 1.2 millimeters. All lie in the schist plane and with longer axes 

 approximately parallel ; so that basal plates, in section normal to c, show- 

 ing the characteristic cleavage at 124 degrees, are rarely met with except 

 in thin-sections cut at right angles to the foliation (common in slides B, 

 F, and G). Bounded inclusions of hematite and zoisite occur in these 

 scales (see figures 1 and 2, plate 62), sometimes in juxtaposition ; epidote 

 also in other slides, generally in grains 0.04 to 0.06 millimeter long. The 

 partial or complete dislodgement of these inclusions during shearing of 

 the schist seems to have resulted in the rounded perforations, which 

 present the same outlines, but are now occupied by the quartz -feldspar 

 mosaic. Scheme of absorption, c > I) > a ; C, bluish green ; Jb, brownish 

 green; a, greenish yellow. Extinction occasionally parallel, on goP^ 

 (100), but 17 to 19 degrees, C /\ c. In slide C, hornblende in grains or 

 short prismatic fragments. In slides B, E, and /, twins, with twinning 

 plane parallel to clinopinacoid, oo P co (010) ; absorption, t) > C > a ; t, 

 deep brownish green ; c, bluish green ; a, straw-yellow. In slide !>, zoisite 

 inclusions as needles parallel to c* axis of hornblende. In slide F, absorp- 

 tion C > t) > a ; C, dark bluish green ; t), brownish green ; a, straw-yellow- 

 In slide H, hornblende reduced to bluish green scales, 0.2 to 0.5 milli- 

 meter in length. In slide /, extinction angle 15 to 16 degrees. 



Hematite (specular iron), generally conspicuous in opaque, splendent 

 scales, iron gray to brownish black, lying in schist plane as irregular 

 groups, 1 millimeter or more in length, sometimes connected in rudely 

 crescentic or hook-shaped masses (figure 2, plate 62). Where most abun- 



