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The Ottawa Naturalist. 



natural crystals. Figs. 3 and 4 will serve to illustrate what we have 

 just been discussing. 



Fig. 3. Fig. -t. 



Fig. 3 illustrates a cube composed of little cubical bricks, some 

 rows of which are removed to shew the resulting step like arrangement 

 of the layers. All the edges of the steps lie in one plane, as seen in 



F'g- 4 



If we remember that the little bricks are supposed to be so minute 

 as to be separately invisible, it will be seen that the steps will appear to 

 lie wholly in the plane, which thus forms a secondary face equally in 

 clined to two faces of the cube. 



Haiiy also shewed how a rhombic dodecahedron resulted 

 from the application of successive layers of these little bricks, each less 

 by one row all round, to the faces of the primitive cube, and of course 

 the same result may be obtained by subtracting rows in the same man- 

 ner. (See Fig 4.) 



Fig. 



He also assumed in some cases that the decrease was parallel, not 

 to the edges of the crystal, but to a diagonal, taking the angles as its 

 point of departure. His theory established the fact that the various 



