Mr, William Phillips on the Oxyd of Tin, 365 



Tenth Modification. 



The planes of this modification replace the lateral solid angles of the 

 primitive crystal, in the same manner as those of the second and 

 ninth, but are still more inclined on the axis passing through those 

 angles, fig. 155. PI. 22. By fig. 156. the planes of this modifica- 

 tion are shewn in a more advanced state, and by fig. 157. in com- 

 bination with the secondary pyramid. Although the planes are of 

 considerable size on many crystals, they are generally rough, or so 

 much rounded, as hitherto to have prevented my obtaining a satis- 

 factory admeasurement of their incidence on the planes of any other 

 modification. 



The crystals represented by figs. 158. and 159. were I believe 

 found loose in a vein near the Land's End. Those of figs. 160. 

 and 162. are from Huel Fanny. That of fig. 166. from Gunnis 

 lake mine : it is about three quarters of an inch in length, and is 

 perfect at both terminations. The crystals delineated by figs. 163, 

 164, 167, 168, 169, 170, and 171, are from Relistian mine. On 

 the crystals, fig. 167. the planes of the first, sixth, and tenth modi- 

 fications were evidently the consequences of a second deposition, as 

 their natural joints with those of the fourth and ninth modifications 

 are visible on every side. 



Eleventh Modification. 



This modification consists in a decrease along the edges of the 

 two pyramids of the primitive crystal, by which each is replaced 

 by a plane ; fig. 172. PI. 23. This plane, by a deeper replacement 

 of those edges, would produce, it will be evident, another and more 

 obtuse octohedron, fig. 173, the apices of which are visible in com- 



