CALCITES OF NEW YORK 21 
the faces of the base or basal pinacoid. Since this form is normal to an 
axis of trigonal symmetry the face resulting from its combination will in 
every instance show trigonal symmetry. 
Prisms. A series of six planes each parallel to one basal axis and to 
the vertical axis will intersect the fundamental rhombohedron in the faces 
which truncate the six lateral solid angles figure 4. In this instance the 
resulting faces are isosceles triangles the vertexes of which are turned 
Fig. 3 Fig. 4 Fig. 5 
alternately up and down. In every case where this prism enters into 
combination with other rhombohedral-hexagonal forms, the resulting 
faces show binary symmetry parallel to the vertical axis. This is the unit 
prism or prism of the first order. 
A series of six planes each perpendicular to one basal axis and parallel 
to the vertical axis, will intersect the fundamental rhombohedron as shown 
in figure 5. These planes which are those of the prism of second order are 
parallel to the lateral rhombohedral edges and in combination with forms 
of rhombohedral symmetry (rhombohedrons and scalenohedrons) produce 
faces of unsymmetrical outline but which are symmetrical in adjacent 
