Ichikawa — Etched Figures of Japanese Quartz. 459 



described in detail. In 1909, I made similar experiments 

 with rock crystal from Kinbuzan, and observed the dull figure 

 formed on each pole of the vertical axis of the etched sphere 

 at the beginning of the corrosion, which is modified as the 

 etching is continued . I also observed a few interesting varieties 

 of the elevations (Aetz-hugel), which may be called ridges or 

 terraces; these are formed on each pole of the vertical axis in more 

 advanced stages of the etching, and can be* modified by the 

 concentration of the acid, etc.* The results of the study of 

 these etched spheres are illustrated in the accompanying plates 

 (III and IV). 



Plate III. {Concentration of hydrofluoric acid, 55 per cent.) 



The dull figures, striations, etc., on the surface of the etched 

 spheres can easily be observed by the naked eye, but the 

 minute study of the ridges, pits, etc., on their surface require 

 a magnification of 75 to 140 times. 



Fig. 1, A, shows a front view of a sphere of a left-handed 

 rock crystal, the dotted line (z z') showing the direction of the 

 vertical axis ; B, is a basal view ; C, that of a pole seen from 

 the other pole. Fig. 2 is a sphere of a right-handed crystal ; 

 A, B, and C corresponding to A, B, and C of fig. 1. Fig. 3 is 

 a sphere of an irregularly developed left-handed Dauphine twin. 

 Fig. 4 shows a sphere of a regularly developed right-handed 

 Dauphine twin ; A, a front view ; B, a basal view. 



Fig. 5 shows the dull figures formed on each pole of a 

 sphere of a right-handed Dauphine twin at the beginning of 

 corrosion ; weak acid was employed. A, is a horizontal projec- 

 tion of a pole of the vertical axis of the sphere ; B, that of a pole 

 seen from the other pole ; the figures do not reveal the direction 

 of rotation. Fig. 6 is a sphere of a left-handed Dauphine twin, 

 A and B corresponding to A and B of fig. 5 ; here, also, the 

 figures do not reveal the direction of rotation. Fig. 7 is a 

 sphere of of a left-handed crystal more etched than those of 

 figs. 5 and 6, thus revealing the direction of rotation ; A and 

 B correspond to A and B of fig. 5. Fig. 8 is a sphere of a 

 right-handed crystal, corresponding to fig. 7. 



Fig. 9 is a horizontal projection of a sphere of an irregularly 

 developed left-handed Dauphine twin. Fig. 10 is a dull figure 

 on a sphere of a regularly developed Dauphine twin ; both 

 poles of the vertical axis are observed horizontally, but when 

 more etched, the direction of rotation is revealed as in fig. 4. 

 Fig. 11 is a plate cut perpendicularly to the vertical axis of a 

 right-handed Dauphine twin, the plate shows the ridges observed 



*See Journal of the Geological Society of Tokyo, vol. xvi, p. 197, 1909 ; 

 xvii, 320, 371, 1910. 



