basaltic hornblende. Tig. 7r. Equilateral fix-fided prifm,acuminated on both extremities by three planes which on one ex tremity are fet on the lateral edges, on the other on the lateral planes; Fig. 78-Six fided pnfm, flady Acuminated on one extremity by tour planes which are fet on the lateral planes on the other bevi led the bevilling planes fet on the two oppofite lateral edges: Fig; 79 Six-fided prifm, on one extremity flatly acuminated by three, planes which are fet on the lateral edges, on the other bevilled, the bevillmg planes fet on the two oppofite edges. CALC SPAR. 1. Six-sided Pyramid. Fig. 80. Double fi* fided pyramid, in which the hteral planes of the one are oblique! y ^ teral planes of the other, in fuch a manner that the ed*es of the common bafis form a zig zag line, and the mdre obtufe lateral edges of the one are oppoied to the lefs obtufe lateral edges of the other pyramid Fig. ai. Preceding figure, acuminated by thiee planes, which are placed on the alternate and obtufe lateral edge^cut^ fix-fided pyramid, acutely acuminated, and the acuminating planes let on the alternate and lefs obtufe lateral edges. Fig. 81 is fig. 80. whofe extremities are very deeply truncate!, and the engles on the common baits alfo truncated; Fig. 84. Preceding figure, m which the fo much that it forms thd^alfage to the next fig 2. Six-