6 RECORDS OF THE ADSTRALTAN MUSEDM. 



figures can be observed ; these are very small but seem to be isosceles 

 triangles with the obtuse angle, which is not much gi-eater than 90°, 

 dix'ected upwards, and the base parallel to the edge 0001/1011. 



The crystal presents essentially the same features as No. viii., and 

 whatever the explanation of these curious features may be it must be 

 applicable to both crystals. 



CiTstal X. (PI. i., fig. 3), Heffernan's Mine, is drawn with a face of 

 p (1011) polar so as to show the structures exhibited by the base to 

 advantage. The sketch represents pai^t of the termination of a crystal of 

 IT) cm. in greatest diameter; foi" the sake of clearness many details are 

 omitted. It will be observed that the upper surface consists of a 

 succession of terraces which are portions of the basal plane bounded by 

 approximately perpendiculai-, deeply fluted walls, with occasional planes 

 of p intervening. The base shows numerous hexagonal markings con- 

 sisting of thin plates bounded by faces of j), as in crj'stals vi. and vii. ; 

 indeed if the residuals were removed and the whole surface of the lowest 

 terrace revealed, or if the " landscape" were restored up to the level of 

 the highest tei'race, the base would then present an appearance similar in 

 all essentials to that of Nos. vi. and vii. A number of horizontal lines 

 will be observed on the prism faces ; these are the outcrops of planes 

 parallel to the base which are present in most of the crystals, most 

 markedly near the terminations, and which, in some cases at least, are 

 continuous across the width of the crystals. Whether these are cleavage 

 planes or planes of growth they probably determine the positions of the 

 successive terraces. 



Crystal xi., fiom Heffernan's, measures 55 X 35 cm. and is of a 

 l)lnish-green colour. It consists simply of base and unit pi-ism. The 

 base is teri-aced slightly and trenched, but not deeply, and the residuals 

 have quite irregular boundaries. Small hexagonal pits appear on the 

 smooth portions of the basal surface. A small quartz crystal projects 

 obliquely from the base; the prism faces of the quartz are fresh but the 

 rliombohedi-al faces are corroded. At one part along the peripheiy of 

 the beryl tlie top layers have been removed, producing a narrow ledge 

 bounded on the inner side by a steep, in parts even overhanging, cliff, 

 slightly embayed. The floor of this ledge is composed of the much 

 corroded base and remnants of the pyramids p and it. It is to be noted 

 that in this specimen, as in all the others, wherever a residual has 

 vertical, or almost vertical, walls bounding it, these are quite rough and 

 irregulai', and are not the faces of prisms ; whenever a residual has 

 sti-aight boundaries these are the intersections of base and pyramid. 



Crystul xii. (IM. ii., figs. 4, 5) also comes from Heffernan's Mine. This 

 tine crystal measures 5-5 X -^'^ ("Ui. and is light green in colour with a 

 yellowish tinge. The only foinis identifiable by inspection are r (0001), 

 (J (1120) and in (1010). The prism faces are striated vertically, and in 

 one place the outer prism layer has been removed to a depth of '3 cm. 

 revealing a new surface underneath ; Iietween the two layers is a tliin 

 selvage of clay, a common feature in zoned crystals fr(mi Heffernan's 

 Mine. l'rol)al)ly this chiyey layer is not an original inclusion but lias 

 been subsequently squeezeil in between the growth shells, 



