GALENA. 155 alluded to in any of Del Rio’s letters to Mr. Brooke, we appre hend that there is some uncertainty with regard to it. The mineral named culebrite by Mr. Brooke is a dark reddish-brown earthy substance, occurring in small thin veins with the riolite from Culebras, and in one of Del Rio’s letters is stated to be ‘ sulphuret of mercury with native selenium, but not combined,’ a description which may probably require to be corrected. SULPHIDES. 47. GALENA.—Galena; Phillips. Plomb sulfure ; Hauy. Hexaedrischer Blei-Glanz ; Mohs. Bleiglanz ; Haiismann. Glanz; Ilaidinger. Cubic. a 100, o 111, d Oil, n 211, m 311, p 122, q 133. ad 00° o' do 35° 16' pa O 0 32' oo' 70 32 na 85 16 po 15 48 dd' 60 0 ma 25 14 qa 76 44 on 64 44 no 19 28 qo 22 0 da 45 0 mo 20 30 FIG. 138. FIG. 139. FIG. 140. FIG. 141. TIG. 142. FIG. 143. Dorms and combinations, a, o, ao, an, aod, non, aom, aodp, aopq. Twins. Twin-face o. Frequently very thin in a direc tion perpendicular to the twin-facc. Cleavage, a, very perfect a ud easily obtained. Fracture conchoidal, seldom observable. li 6