586 MINERALS AND VEINS OF jEGIRINE-SYENITE, 



(l)This type is typical of the class and shows well defined 

 border zones on either side, about - 5 cm. wide, composed of stout 

 sanidine crystals arranged normally to the sides of the fissure; 

 the main body of the vein, within, has a finer-grained texture 

 than that of the preceding classes, but is yet much coarser than 

 the parent syenite traversed. The sanidines of the core towards 

 its margins, in proximity to the prismatic zones, are conspicuously 

 arranged in flow structure; towards the interior, it assumes a 

 pilotaxitic arrangement in which segirine and arfvedsonite are 

 subordinate, the latter noticeably more abundant towards the 

 centre (Pl.xlix., fig. 2). The flow structure argues introduction in 

 a viscous state with felspars previously formed or contempora- 

 neously crystallising out. Corrosion and corrasion of the inner 

 extremities of the sanidines forming the prismatic border zone is 

 sufficient evidence that they are not crystallisations from the 

 central filling but formed at an earlier period, either sweating 

 from the sides or proceeding from less viscous solutions. 



Uralitisation and carbonation are both to be noted, though not 

 sufficiently extensive to materially affect its characters. 



(2) In the carbonated syenite of Loveridge's main quarry, 

 parallel-sided veins about 2 cms. wide were noted, of a uniform 

 colour slightly darker than the rock traversed. At first glance 

 they appear to be of an entirely new class. Carefully examined, 

 they show close analogy to that just described, A much corraded 

 prismatic border zone and a central filling with flow structure 

 towards the margin. Like the body of the rock in the neigh- 

 bourhood, however, it has been bleached by extreme carbonation 

 and its salient characters thereby somewhat obliterated. 



Abundant siderite and leucoxene are all that remain of the 

 ferriferous minerals; secondary chalcedony and silica compose 

 about twenty per cent, of the material, their preponderance sug- 

 gesting a primary origin which, however, cannot be reconciled 

 with their petrographical relations. In places where sanidine 

 crystals are embedded in chalcedony, they frequently show a 

 narrow marginal zone of what appears to be a slightly more acid 

 felspar extinguishing alike with the original individual. 



