270 



University of California. 



[Vol. 3. 



face. The etch figures are usually triangular in shape and vary 

 in size from a maximum length of about three millimeters and 

 width of one millimeter to ones of miscroscopic size. Not infre- 

 quently there will be several smaller ones in the base of a larger 

 one . 



Occasionally a long string of the figures will run across a 

 prism face, in an approximately horizontal direction. ■ 



The orientation of these triangular pits with reference to the 

 cry stallo graphic directions, varies somewhat but, in general, is 

 fairly constant and is shown in Fig. 1. The position of these 



figures on the four prism faces is shown in Fig. 2. It is noticed 

 that they always point away from the orthopinacoid and the 

 angle nearly 90° is nearest the clinopinacoid. Rarely the 

 triangle passes into a trapezium by the addition of a fourth side, 

 as is shown in the middle figure of Fig. 1; very few of the edges 

 are perfectly straight, being more or less rounded, but they are 

 mostly all drawn straight. 



Fig. 1, Plate 27, shows a photomicrograph of the common 

 appearance of these etch figures — a large number of imperfect 

 ones closely crowded together. Fig. 2 shows a view of the best 

 group of etch figures that could be found on any of the crystals. 



Fig. 1. Showing position of 

 etch figures on unit prism face 

 (110). 



Fig. 2. Showing position of 

 etch figures on the four unit 

 prism faces. 



