as
it were, cut off, and new ones produced in their place, which properly
belong neither to the one form nor the other, but are edges or angles
of combination. Usually, one form predominates more than the others, or
has more influence on the general aspect of the crystal, and hence is
distinguished as the predominant form, the others being named
subordinate. The following terms used on this subject require
explanation. A combination is developed when all the forms
contributing to its formation are pointed out; and its sign consists of
the signs of these forms, written in the order of their influence on
the combination, with a point between. An angle or edge is said to be replaced when it is cut off by one or more secondary planes; it is truncated when cut by one plane, forming equal angles with the adjacent faces; and an edge is bevelled when replaced by two planes, which are equally inclined to the adjacent faces.
It
will be readily seen that such combinations may bo exceedingly
numerous, or rather infinite; and only a few of the more common can bo
noticed, simply as specimens of the class. Many others more complicated
will occur in the descriptive part of this treatise. Among
plenotesseral combinations, the cube, octahedron, and also the
rhombic-dodecahedron, are the predoniinant forms. In fig. 16 the
