406 Mr. WHEWELL on the Classification 
RHOMBOHEDRAL SYSTEM. 
Remarks. 
Example and Figure. Class. Combination. 
Class III. pR, qRr 
OR, Rr} No. 3. OR, qRr 
or 
This position of the faces | Rh’. Emerald-mal.2R,®Rr| No. 4. pR, @Rr 
of the prism, easily distin- | Mohs, Vol. II. 118.7 s 
guishable from I. 4. shews > 
that the prism is © Rr, and 
not «R. 
The form of the faces of aR, pRr 
the prism distinguishes it 
from Rr, as in VI. 2. 
Rh’. Fluor-haloide ® R, eRr oR, oRr 
II.149. e M 
pRm, gRu 
If edges of combination of | Rh’. Lime-haloide, R3,R5| No. 1. pRm, pRn 
two pyramids are parallel to 
lateral edges, the first index 
is the same for both. 
TE GS 3 sy 
If edges of combination 
are horizontal, the second 
index is the same for both 
pyramids. 
Rh’, Lime-haloide, +R3,R3| No. 2. pRm, gRm 
TE 190.4, fb # 
R3, oR No. 3. pRm, ORn 
Fito 
Rh’. Fluor-haloide R3, oRS No. 4. pRm, 2 Rm 
II. 148. > ¢ 
