8 RECORDS OK THK AU.STRAMAX MCSEDM. 



Penlield^ has described a similar feature in tlie case of the berjl of Mt. 

 Aiitero, California, and ascribes the formation of certain very steej) 

 pyramids to solvent action. He was able to identify one of the pyramids 

 as the form (o(v24-60 5) ; in the case of tlie Torrington beryl no planes 

 are recognisable. 



luterprctiiliini «f //"' Murl.iinj^: <nt the llidic. — Regular markings, 

 whether pits or hillocks, on the faces of crystals may be caused by 

 solution, or may be growth features, and it is not always easy to decide to 

 which of these the markings are to be attributed in particular cases. 

 Professor V. Goldschmidt, who has had much experience in this branch 

 of .crystallography, says'': — "Oft ist es scliwer, nianchmal unmoglich, 

 Losungstiguren und Wachstumstiguren zu unterscheiden. Ks wird unsere 

 Aufgabe seiii Kriterien zu dereu Unterscheiduug festzulegen. So lange 

 wii- nicht fiir die eiuzelne Figur entscheiden kriunen, betrachten wir 

 dei-lei Gebilde als Losungstiguren, wenn ihre Gesamtheit daiuuf schliesseu 

 liisst, dass die Bildungsgescliichte des vorliegenden Krystalls mit Lcisung 

 abgeschlossen hat, umgekehrt als Wachstumsfigureu, wemi wir aus alien 

 Anzeichen schliesseu konneu, dass sie mit Wachsen abgeschlossen hat." 



In tlie case of the Torringtou beryl, cr3'stal xii. (PI. ii., figs. 4, 5) has 

 clearly been etched by some solvent. The pits are precisely similar to 

 the artificial etch figures which can be developed on the base when the 

 ci'ystal is immersed iu fused caustic soda for example. It is also pretty 

 certain that ciTstals xiv. and xv. have undergoiie considerable solution, 

 and indeed represent a late stage in the process ; in fact, we may fairly 

 conclude that the closing chapter in the history of these ciystals was 

 one in which solution played a leading i-ole, which prima facie would 

 indicate that the peculiar features of crystals viii.-xi. are also the result 

 of solution. Again, the narrow baud shown between the pyramids and 

 prisms in crystal No. i. (PI. i., figs. 1, 2) is undoubtedly etched, and the 

 fact that in crystal v. the pyramid faces have been almost obliterateil 

 indicates that the etching is progi'essive. It is in accordance Avith theoiy 

 that dissolution should be most active along pi-ominent edges, and that 

 these should be first attacked. While it is clear that solution has taken 

 [ilace in these crystals 1 hesitate to state dogmatically that crystals viii., 

 ix., X., aud xi. owe their striking appearance to a process of etcliing, and 

 must leave the decision to those who have more experience of ciystal 

 solution and growth. 1 shall content myself Avith stating the facts and 

 indicating possible deductions therefrom. 



In these ciystals the pyramidal faces which bound the hillocks are 

 smooth and brilliant, with little oi- no suggestion of the curvature and 

 stiMation which Ave associate Avith solution faces ; moreover, in etching 

 experiments it has been found that the figure faces usually have high 

 indices and are indeed vicinal in character. Yet regarding crystal Nt». 

 viii. (PI. ii.. Hg. 7) one (ran scarcely resist the conclusion that the 

 gullies and pits which now diveisify its surface are secondary, and, if that 



■"' P«'ntiol.l— Aiuer. Journ. Sci.. xl., 1890. pp. 488-4.90. 

 * (joldbchiiiidt — Zeitb. Krybt., -xl.. 1, 1905, ji. y79. 



