DALY. — ETCH-FIGURES ON AMPHIBOLES. 399 



The Kragero sub-type differs, then, from the Wolfsberg sub-type in 

 the hick of curvature in the figure-face A D D A\ in the acuteness of 

 the northeast angle at A, in the greater variation of shape as the figure 

 grows older, and in the stoutness of the figure in plan. The orientation 

 is the same in both, as also the occurrence of the adventitious fourth 

 figure-face adjoining G E in the figure (see Plate I. Fig. 10). V. 42 is 

 the only other amphibole that showed closely similar etching phenomena 

 (Plate I. Figs. 11 and 12, and Photograp»h 3), but their clearness has led 

 to the conclusion that we have here a new category of figures whose ex- 

 planation should be looked for in the internal structure of the varieties in 

 question. The lack of analyses forbids the extension of this hypothesis. 



The Edenville Sub-type, (110). 



Edenite gave abundant figures, apparently identical with those on the 

 Wolfsberg hornblende, but the habit of a cleavage piece of the former 

 was peculiar in exibiting a general predominance of the four-sided figures 

 already noted in connection with the previous two sub-types (Plate I. 

 Figs. 13 and 14). The triangular figures do occur, but their number is 

 quite subordinate. Even without their aid, it is very easy to orient cleav- 

 age plates of the mineral by means of fairly well developed quadrilateral 

 figures ; in them, the upper end is always recognizable. 



The PkiUpstad Sub-type, (110). 



The last of the hornblende sub-types which we have to notice is of 

 special interest, since it led at once to further investigation and the dis- 

 covery of a new and interesting variety of amphibole. Figures were 

 produced on four different crystals, with exposures of 2 min., 2 min., 

 1| min., and 2 min., respectively, and on another crystal immersed in 

 hot HF (near its boiling point) for one minute. In all five, the result 

 was the same, two clearly defined figures, whose distribution was at first 

 a mystery ; on further study it was found that one type was confined to 

 the cleavage faces and the other to the crystal faces, or to cleavage surfaces 

 lying not more than 1 mm. beneath the latter. We begin with a de- 

 scription of the first mentioned sort of figures. 



They vary in number of sides, in tint (proportion and distribution of 

 light and shade), and considerably in shape (Photographs 6 and 7). 

 Usually, they are six- or seven-sided and bounded by nearly or quite 

 straight edges (Photograph 6), and either uniformly dark or more or less 

 brilliantly illuminated on certain figure-faces. I could get no satisfactory 



