EXPLANATION OF THE FIGURES 



Inasmuch as the brevity of my hurried writing has left not a few 

 things insufificiently explained, especially where the treatment con- 

 cerns angular bodies and the strata of the earth, in order to afford 

 some sort of remedy for that defect, I have decided to add here the 

 following figures, chosen from very many others. 



[Plate IX] 



The first thirteen figures, intended to illustrate the angular bodies 

 of crystal, fall into two classes. 



The first class contains seven varieties of a plane in which the 

 axis of the crystal lies. 



In figures i, 2, and 3, the axes of the parts, of which the body of 

 the crystal is composed, form a straight line ; but there is an inter- 

 mediate prism, which is lacking in Figure i, appears rather short in 

 2, longer in 3. 



In Figure 4, the axes of the parts which make up the body of 

 the crystal do not form a straight line. 



Figures 5 and 6 belong to the class of those which I could pre- 

 sent in countless numbers to prove that in the plane of the axis 

 both the number and the length of the sides are changed in various 

 ways without changing the angles ; that various cavities are left in 

 the very middle of the crystal, and that various layers are formed. 

 Figure 7 in the plane of its axis shows how both the number and the 

 length of the sides are sometimes increased in various ways, some- 

 times diminished, from the new crystalline matter placed above the 

 planes of the pyramids. 



The second class contains six varieties of base of planes.^ 

 In Figures 8, 9, 10, and 1 1, there are only six sides ; with this dif- 

 ference, nevertheless, that in Figure 8 all the sides are equal, while 



^ The cross section parallel to the basal pinacoid. 

 272 



