1880.] NATURAL SCIENCES OF PHILADELPHIA. 251 



Ripidolite. 



1. Patterson's Quarry, Xewliu Township, Chester 



Co., Pa. Irregular green plates; with corun- 

 dum ; inclination of bissectrix to normal to 

 cleavage plane, 5^30': optic-axial divergence 

 variable on the same plate on account of twin- 

 ning, varying from 50° to 59°30'. (T. D. 

 Rand.) Generally as given. 59°30'. 



2. West Chester, Pa. Green plates ; inclination of 



bissectrix 10° : axial divergence, 78°3'0'. 



3. Brinton's Quarrj', Chester Co., Pa. Fine clear 



green plates ; inclination of bissectrix, 12°30'. 



f) y> V. Axial divergence, 82°. 



4. Dudleyville, Ala. Pale rose-color; on chromite. 



Inclination of bissectrix, 1G°. o > v. (F. 



A. Genth). 94° 15'. 



In all of these, double refraction is feeble compared with that of 



Muscovite. It is observed that the inclination of the bissectrix 



to the normal to the cleavage plane increases with the divergence 



of the optic axes. 



Prochlorite. 



Brewster, X. Y., Tillj- Foster Mine. Uniaxial. 0°. 



Margarite. 



1. Cullakanee, N. C. White, "altered from corun- 



dum." Irregular figures. (F. A. Genth.) 110°±. 



2. Chester, Mass. Rose-color, with corundum ; 



irregular, in some places showing four hj^per- 



bolas; one piece gave 89°30'. 1I2°45'. 



3. Dudle3'ville, Ala. White, clear; inclination of 



bissectrix, 1°±. (F. A. Genth). 122°15'. 



4. Cullakanee, X. C. White, " altered from Zoisite." 



Inclination of bissectrix to normal to cleavage 

 plane, 2°ih. (F. A. Genth.) 124°. 



The large optic-axial divergence of Margarite readily distin- 

 guishes it from Damourite and other micas which resemble it. If 

 further observations agree in showing that the bissectrix is inclined 

 to the normal to the cleavage plane, it will show that Margarite 

 is Monoclinic and not Orthorhombic as has been supposed. 



