i9o6] TRAVIS— PYRITE FROM CORNWALL. 145 



(221) and (774) were observed on crystal 23. They were ex- 

 tremely narrow faces, each lying in a zone with (211) and a diploid. 

 Their narrowness prevented their giving any definite signal, but 

 they were very perfect and gave fairly good results by direct observa- 

 tion, that is with the small auxiliary lens down in front of the tele- 

 scope objective. There was no doubt as to the diploid determining 

 (211). It gave, — 



321 [\ III. 



Measured 22° 13' 



Calculated 22° 12 



but the one determining (774), that is (i 1.8.5), was not definite. 

 This problem was solved by measuring the angle between the zones 

 (211) (774) and (2ii)(iii) on a petrographical microscope read- 

 ing angles to 5'. 



121 /\ 221. 



Measured 11° 36' 



Calculated 11° 3o' 



121 /\ 774. p </• 



Measured 43'' 39' I7° 01' 



Calculated 44'' 01' 17° 05' 



The remaining trisoctahedron (552) will be discussed along 

 with the trapezohedron (744) for a special reason. 



(211) is of common occurrence and cannot be mistaken, on ac- 

 count of its striation. It usually gives a poor reflection. A measure- 

 ment on crystal 22, however, gives, — 



211 /\ III. 



Measured I9° 28' 



Calculated I9° 28' 



(744) and (552) were observed on crystal 24. The pyritohedron 

 (210) and the octahedron are present, and two faces of (321), one 

 of which lies in a zone with (210) and (m). The two faces con- 

 sidered lie in a zone with (210) and the other diploid face (132). 

 They are both extremely narrow, (744) not being wide enough to 

 afford a satisfactory signal, and requiring measurement by direct ob- 

 servation. 



210 A 474- 210 A 552. 



Measured 42° 23' 23° 48' 



Calculated 41*' 49' 24° 06' 



