Yol. 57.] 



AMONG THE MALVEEN CAMBEIANS. 



161 



Fig. 1. — Cross-section of a com- 

 pletely -resorhed plienocryst of 

 am2)hibole from caniptonite 

 (M 209), showing prisms and 

 clinopinacoids. x 110 diam. 



rig. 2. — Camptonite (M4S9 a J. 

 X 22 diam. 











"*^ 





^4%*; 



A needle of colourless ainpliibole, 

 showing the asbestiform condition. 

 Sections of other needles (including 

 a cross-section near the bottom of 

 the figure) are visible. Most of the 

 grey granules in the groundraass are 

 augite ; the black are iron-ore. In 

 places the flow -arrangement of the 

 minute felspar-laths is shown. The 

 ' white patch is an imperfection in the 

 section. 



Q. J. G. S. No. 225, 



is a colourless substance,, 

 usuallj' isotropic, or polarizing 

 in weak tints, or occasionally 

 more strongly, which occurs in 

 irregular patches or small crys- 

 tals in the groundmass, and 

 sometimes in the phenocrysts. 

 In the former case it often 

 presents somewhat the appear- 

 ance of a colourless glass. But 

 apart from the improbability of 

 a clear glass being present in 

 greatly altered rocks of basic 

 composition, the analogy of 

 other rocks (see p. 171) makes 

 it very probable that the sub- 

 stance is, at any rate in part, 

 analcime. 



A few details as to the cha- 

 racter of the prevailing minerals 

 may now be given. 



The amphibole (PL VII,. 

 figs. 5 & C) ; and text-figs. 1 

 & 2, also text -fig. 5, p. 165) 

 occurs in two forms, both idio- 

 morphic in the prism zone, with 

 the prismatic faces well-deve- 

 loped and the clinopinacoids 

 either large or small. The 

 prevailing forms are short or 

 long needles ; less common are 

 short stout prisms, apparentl}- 

 showing the shape of basaltic 

 hornblende (PI. YII, fig. 5) 

 with terminal faces. These 

 are generally larger than the 

 needles, and are frequently cor- 

 roded. They would appear to 

 be undoubted phenocrysts. 



The needles sometimes attain 

 a considerable size (text-fig. 2), 

 the largest seen measuring 

 y^ inch ; but these are few in 

 number, and the crystals are 

 mostly small and not intri- 

 cately corroded. It is difficult 

 to say whether terminal faces 

 are present or not. Two or 

 three needles occasionally inter- 

 penetrate one another. The 

 needles are usually very much. 



