412 Mr. WHEWELL on the Classification 
RHOMBOHEDRAL SYSTEM. 
Remarks. Example and Figure. Class. Combination. 
Class IX. Double 
When plagihedral faces Plagihedral. 
are thus distributed, the for- 
; No. 1 
mula ist . | ipRm, pRn} 
No. 2. 
7 Be = {pRm, pRn} 
When plagihedral faces Rh!. Fluor-haloide. No. 3. 
are thus distributed, the for- Rr, RR, = {RE RLY = {pRm, pRn} 
mula is ria te - b 
Mohs II. 149. 
SQUARE-PYRAMIDAL COMBINATIONS. 
Remarks. Example and Figure. Class. Combination. 
Class I. |pQ,gQ& pQ,qQr 
No. 1. pQ, 2pQr 
Square Pyr’. Zircon Qr, Q 
or pQr, pQ 
Mohs, Vol. II. 99. ¢ P 
Square Pyr'. Garnet Q, 2Q PQ, 2"pQ 
II. 96. ¢ 6 
Sq. Pyr'. Lead-baryt £Q, 0Q pQ, 0Q 
II. 92. 6 a 
Sq. Pyr'. Tin-ore Q, ©Q PQ eQ 
II. 102, p 1 
