364 Mr. William Phillips on the OxydofTin, 



ficatlon, exhibit its planes very differently, and on all the crystals 

 represented by these two figures, they are so uneven, or irregularly 

 striated, as to render it wholly impossible to subject them to the 

 reflecting goniometer. This modification is extremely rare. The 

 crystals described by fig. lOS. have I believe been brought only 

 from the mine called Huel Fanny, west of Redruth. 



Nltith Modification. 



By the ninth modification, as well as by the second, each of the 

 four solid angles formed by the meeting of the tw-o pyramids of the 

 primitive form, is replaced by two triangular planes, placed on the 

 edges of the pyramid, and inclining on the axis passing through 

 the solid angles ; but in this modification they incline more on that 

 axis than those of the second modification, fig. 110. PI. 20. 



Fig. 111. shews the planes of this modification in a more 

 advanced state; and fig. 112. shews them in combination with the 

 secondary pyramid. They are generally so minute or so consider- 

 ably striated, as to prevent their incidence either with the planes of 

 the primitive form, or with those of any other modification, from 

 being satisfactorily obtained. 



The greater part of the crystals delineated in the series of this 

 modification, of which the planes of the first modification are long, 

 and on which those of the seventh modification are observable, were 

 taken from the surfaces of rounded portions of grauwacke, found 

 in the hollow parts of the vein in Relistian mine. I have not 

 noticed any macles on the specimens from that mine ; all the 

 crystals from it are nearly black, and of remarkable brilliancy.. 



