424 //. A. Miers — Quartz from North Carolina. 



11 = 18.3. 8 =^fPff 

 = 25.5.11 =i-i-P% 



The former replaces the edge between u and 3R on a crystal 

 from Wallis (fig. 27) ; the latter replaces the edge between s 

 and an acute rhombohedron to which the symbol 8R is ascribed, 

 on a crystal from Wallis (fig. 41) ; both forms are, it is true, 

 somewhat doubtful, and no numerical measurements are given 

 for the face ; it is in fact quite possible that the latter may 

 be identical with 2 of the present crystal. 



If 2 belongs to the zone sll it must have the symbol : 



32.7.14 = j- JP-ff = 39.7.46.11 



The angular values corresponding to this symbol are given in 

 the last column of the preceding table and approximate very 

 closely to the observed angles ; in fact it is scarcely possible 

 from the above observations alone to distinguish between the 

 two symbols. 



Now the measurements are perfectly reliable, both 1 and # 2 

 being bright faces which yield very sharp reflexions. X is 

 smooth, and # 2 is slightly striated in a direction almost coinci- 

 dent with the edge X $ 2 



In order to establish with accuracy the zone X 2 we may 

 seek to determine the acute rhombohedron which it contains. 



Between 3R, which is a brilliant face, and the prism g a is an 

 acute rhombohedron Y x . 



3E : T x = 12° 22-J' 



3-R:f/ a 14 27 (calculated 14° 42±') 



further 2 lies in a zone with X and 1T X . 



Now since the angle SR:g a differs by 15J-' from its calcu- 

 lated value, and the face SR yields the better reflection and is 

 free from striations, we must determine the indices of Y x from 

 its inclination to k 6R, disregarding g a Hence 



T 1 = 1SE 3R : 1872 = 12° 1 4-J-' (calculated). 



Assuming the indices 



# = 40.5.17, #— 23.5.10 



the zone X 2 contains the rhombohedron 76.35.35 == ^lR 

 which is inclined to SR at the angle 12° 16J' and therefore 

 practically coincides with Y v 



If, on the other hand the indices of _$ 2 are 32.7.14 the zone 

 X 2 contains the rhombohedron 104.49.49 = - d j-R which is 

 inclined to 37? at the angle 12° 56£'. 



Hence there can be no doubt that the symbol of the new 

 face is 



<£„ = 23.5.10 



