HOBBS MINERALOGY OF WISCONSIN. 147 



on all of the three crystals are c, rf, e, and a. The new forms 

 lying in the principal zone were easily determined from 

 their angles with the basal pinacoid. The forms e and b 

 were determined, the former from its angle with c and 

 with 010 (one-half the angle e : e over the end of the ~b 

 axis), the latter from its angle with c and with both e 

 and b. 



The forms observed on the three crystals are given 

 below, those that are new to the species being marked by 

 an asterisk: 



Forms. Crystals. 



c, OP (001) I II III 



a, ao Poo (100) I II III 

 *, Poo (101) I II III 

 c, --fPoo (307)* III 

 6, Poo (101) I III 



b, IPoo (203)* II 

 n, iPoo (102) II 

 o, IPoo (205)* I II 



6, iP2 (245) I II III 



(9.12.8)* II III 



The average of several measurements of the interfacial 

 angles of the planes of the above forms are given below. 

 The reflections from the pyramid faces are fairly good, but 

 in the principal zone the measurement is made difficult by 

 striation, particularly on the faces 6, a, and n, and by a 

 curvature, or better warping, apparently caused by the in- 

 tergrowth of nearly parallel individuals. This explains 

 the considerable variation between the readings of angles 

 and their calculated values, as indicated in the parallel col- 

 umns of the following table. 



