28 THE GRANITE INTRUSIONS 



granite and a gneiss, in which the foliation structure 

 can be seen in even a small fragment, can be found ; 

 the massive granite is seen in the interior of the area 

 and the foliated rock near the periphery, but this rule is 

 not without many exceptions. There is no general dif- 

 ference in mineralogical composition between the granite 

 and gneiss ; the structural characters which separate the 

 gneiss from the granite seem to have been given to the 

 rock during its consolidation, for the gneiss does not 

 show evidence of a great amount of crushing or rear- 

 rangement of its component minerals after it solidified. 

 The foliation planes lie in the same direction as the 

 strike and cleavage of the sedimentary rocks in the 

 neighbourhood ; a similar direction is at places observed 

 in the arrangement of the large porphyritic crystals of 

 orthoclase that are occasionally found in great numbers 

 in the massive granite, which shows no other parallel 

 structure. There is no evidence of a difference in age 

 between the granite and gneiss, and the gradual coming 

 in of the gneissose structure as the area is traversed in 

 various directions points to the whole mass being the 

 product of one period of igneous activity. 



Large and small veins or dyke-like bodies of micro- 

 granite and quartz-porphyry with a micro-granitic base 

 are found towards the edge of the area in many places. 

 Near Hoetjes Bay the quartz-porphyries are especially 

 abundant. Near Darling a mass of quartz- porphyry 

 has a well-developed parallel structure, and may be con- 

 sidered to bear the same relation to the massive quartz- 

 porphyry as the gneiss does to the granite. 



In the hills to the south and west of Darling there 



