292 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



minerals have developed in the sedimentary rocks, the most con- 

 spicuous being garnet, staurolite, cyanite, and hornblende. The 

 hornblende is a common product of this metamorphism, especially in 

 the calcareous rocks of the Wallace (Newland) formation. A speci- 

 men from west of the West Sister peak, Avery quadrangle (ll-J-61 

 "hornblende" collected by E. L. Jones, jr., July 27, 1911), consists 

 of black blades making up sheaves 2 cm. long by 1 cm. in maximum 

 width. These sheaves are abundant in a cherty matrix which looks 

 like limestone in the hand specimen but which contains no car- 

 bonate. Under the microscope the hornblende is very pale colored, 

 though probably faintly pleochroic in tones of blue-gray and brown, 

 but this is obscured by the presence of very abundant inclusions. 

 It is biaxial negative (-) with 2V large. The extinction Zac is 16° 

 to 17°. The refractive index, /3 is about 1.629. 



Another specimen of similar material from northwest of the 

 Sisters (ll-C-85 "amphibole rock" collected by Calkins, July 29, 

 1911, notebook No. 2, p. 5) consists very largely of sheaves and 

 tufts of glistening black blades in a gray matrix which contains 

 some carbonate. Under the microscope this hornblende is practically 

 colorless, but is crowded with minute inclusions. The extinction, 

 Zac is 18° and the refractive index, /3 is 1.630. 



A third specimen from the same general region (1 l-J-63 " Elevation 

 3,700 feet, in Creek, see traverse," collected by E. L. Jones, jr., 

 July 27, 1911) is a somewhat waterworn mass from the stream bed. 

 It consists of silky lustered greenish-black blades up to 1 cm. long 

 by 5 mm. wide and 3 mm. thick, thickly disseminated in a scaly 

 purplish base. The hornblende is biaxial negative with 2V large, 

 dispersion r<v weak; extinction Zac is 11°-14°. It is pleochroic 

 in pale colors, X = brownish-green, Y= greenish-brown, Z = bluish 

 gray-green. The refractive indices are approximately a = 1.650, 

 0= 1.660, 7 = 1.669. The purplish matrix of this hornblende consists 

 of about equal parts of fine granular quartz and a pale brown uniaxial 

 negative pleochroic micaceous mineral, doubtless biotite, and a few 

 isotropic grains of colorless garnet. 



HUDSONITE 



VARIETY OF AMPHIBOLE 



Silicate of ferrous iron with lime, Monoclinic. 



alumina, ferric iron, etc. 



CUSTER COUNTY 



A specimen, sent to the National Museum for identification by 

 P. H. Rasche from Stanley, Custer County, consists mainly of an 

 unusual amphibole having optical properties and composition 



