40 



MINERALOGY 



the development of the crystal to be illustrated, as all faces may 

 be moved back and forth on any axis, if their inclination be not 

 changed. The intersection of d with the edge of the pyramid is 



* 



FIG. 62. 



found by drawing c'cc" parallel to the axis & ; where this line inter- 

 sects the edge of the pyramid at c' will be a point common to both 

 the edge of the pyramid and the base ; likewise c", the intersec- 

 tion of c and p, will be parallel to pp' as the two edges belong to the 



