20O 



HOLLAND : SIVAMALAI SERIES. 



oftener they and all the other constituents present no definite crystal 

 faces. 



Fig. 4— Crystal of olivine ', partially enveloping green augite in laurvikite. 

 Rock No. 111463, magnified by 40 diameters. 



As already stated, the felspars are mainly microperthite^ similar 

 to that in the elaeolite-syenite ; but often, especially in the coarse- 

 grained forms, there are very complicated intergrowths of a well 

 twinned plagioclase with either common microperthite or with micro- 

 perthitic microcline. The individuals interlock with very irregular 

 borders, but show no constant tendency to extension along any 

 definite crystallographic direction. 



The green augite is scarcely pleochroic in thin section, but 

 shows a series of well-defined gliding planes often accompanied by 

 lamellar twinning. 



The hornblende is partly the common, highly pleochroic, brown- 

 ish-green variety which in cross-section often shows traces of the 

 forms (no) and (010). Other crystals present the characters of 

 Brogger's barkevikite. 



The olivine forms rounded irregular lumps with finger-like exten- 

 sions (fig. 4). There is a tendency to grouping in rich patches, and 



( 32 ) 



