396 Mr. Wuewe tt on the Classification 
of combination will be exemplified in the figures referred to; and 
we shall also give instances where these combinations, either alone 
or united with others, have been observed among minerals. For 
this latter purpose, the references will be made to Mohs’s Crystal- 
lography, the name of the mineral and the number of the figure 
being mentioned. 
Hence, in the following tables, the principal columns are those 
two which, for the sake of convenience in printing, are put the 
last. The one containing the symbol of the combination, and the 
other the resulting properties. The columns which are placed 
before these, contain the Class and Number of the Combination 
ot which we speak, the examples of its occurrence with their 
symbols, .and such other observations as are requisite for the 
purpose of distinguishing among resembling combinations, or any 
other circumstances proper to be remarked. 
As the words Edges of Combinations occur very frequently. 
the abbreviation E. C. is used to represent them. 
The preceding Theorems are referred to by means of the 
letters (4), (B), &c. by which they are here distinguished. The 
Subsidiary Theorems are marked with the class and number of 
the combination to which they belong. 
SUBSIDIARY THEOREMS. 
Rhombohedral System. 
Crass II. Comb. 4. Let pR’ and gRm be the forms. Then, 
in order that pR’ may truncate the acute terminal edges of gRm, 
we must have the truncating pyramid pR’, equivalent to one 
which has its axis (OV’, Fig. 1.) equal to that of the truncated 
re 
