366 



Review of Dana's Mineralogy. 



It 



is a 



Fig. 3. 



Following the order of his crystallographic system, Mr. Dana 

 unfolds this intricate subject by a beautiful series of figures, of 

 which we can notice only the following : — 



" Figure 3 represents a crystal of Galena from Rossie. 

 shortened cube ; the lateral faces are very irreg- 

 ularly curved, and consist of the primary faces 

 of the cube and the planes truncating the lateral 

 edges. Some of the terminal edges are also 

 truncated. The crystal is surrounded by a low 

 pyramid, consisting of four planes on each of the 

 angles and edges, which, owing to the distortion, 

 do not occur elsewhere on the crystal. The 

 cleavages of the crystal easily explain the relations of the several 

 planes to the primary." 



" Figure 5 of apatite is the same form that is represented in figure 4, 

 but greatly distorted. The planes e', e, e", between P and the right M, 



Fig. 4. 



Fig. 5. 



are enlarged, while the corresponding planes below are in part oblitera- 

 ted. By observing that similar planes are lettered alike, the two figures 



may be compared throughout." 



Fig. 7. 



Fig. 6. 



" Curved Crystals. — Curves in imbedded crystals are of frequent oc- 

 currence ; and in implanted crystals they are not very uncommon. The 

 annexed figure of quartz, (fig. 6,) illustrates this kind of distortion ; the 



