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On the right of the section 

 are nine roughly parallel 

 veins (ab) of a crystalline 

 rock (a & b in the previous 

 paper) cutting the normal 

 hornblende - granite. The 

 veins are only a few inches 

 thick, generally about 3 

 inches. They are composed 

 of quartz-norite with sub- 

 ordinate biotite, hornblende, 

 and monoclinic pyroxene. 

 The felspar is mainly plagio- 

 clase, but enclosed in the 

 crystals of plagioclase are 

 small prisms which may be 

 orbhocluse. A separation, 

 however, of the rock-con- 

 stituents in iodides of mer- 

 cury and potassium did not 

 yield any orthoclase. 1 The 

 rhombic pyroxene in good 

 sections is almost colourless, 

 and rarely can any pleo- 

 chroism be observed. But, 

 in thick sections and in 

 grains separated from the 

 crushed rock, it is seen to 

 be coloured, and to give the 

 characteristic pleochroism of 

 rhombic pyroxenes. The 

 position of the acute bisec- 

 trix could not be determined 

 with certainty, nor could 

 sufficiently clean material 

 be separated for an estima- 

 tion of the iron contents. 



3 A little felspar of the same 

 specific gravity as quartz was 

 obtained (2*66) : the rest was 

 slightly heavier. The maximum 

 extinction-angle on sections per- 

 pendicular to the twin lamellae 

 was 23°. This points to the 

 greater part of the felspar being 

 between andesine and labradorite. 

 The maximum extinction-angle 

 observed in the plagioclase of 

 the normal granite was 14°. In 

 the pyroxene- raicrogranite the 

 extinction-angle shows that some 

 of the felspar approaches that 

 in the quartz-norite. 



