43 



Before crystallization was completed the tranquillity of 

 the intratelluric magma was violently disturbed by earth 

 movements, and injection took place. In the course of these 

 events portions of the solidified — or almost solidified — quartz 

 mica diorite came to be engulfed in the partially ci^ystallized 

 granite, and so now the granite contains fragments, both 

 small and great, of the diorite, including the two great masses 

 on Granite Island; these fragments really play the part of 

 "basic secretions" in the granite, though indeed the term 

 is somewhat of a misnomer, seeing that the included 

 rock has actually a greater percentage of SiOj and more free 

 quartz than its host.^^^) 



The intercrustal magma must have been tapped near its 

 base, seeing that we find tlie porphyritic granite invaded by 

 the more acid and lighter even-grained granite. 



Tliese magma fractions then, having been injected into 

 the secondary magma chamber (their present position), con- 

 tinued to ciystallize under the new conditions. Hence in the 

 granite we get the second generation of crystals forming a 

 groundfc-mass or matrix to the first-formed phenocrysts. The 

 residual liquid from this last crystallization was later squeezed 

 out into cracks, forming the narrow aplitic dykes cutting the 

 granites and diorite, so that these are the only products of in 

 situ differentiation. The even-grained granite may have 

 scarcely started to crystallize before injection (it has been 

 noted above that the constitution of this rock is similar to 

 that of the matrix of the porphyritic granite), and the new 

 conditions caused it to solidify in even-grained fashion. 



It is a far cry from this highly potassic rock to the 

 highly sodic albite syenite, and possibly one or more of the 

 intermediate stages are missing, but at all events the residual 

 syenite magma, perhaps partially crystallized and highly 

 charged with mineralizers, was finally forced upwards, rifting 

 off blocks of schist and sending apophyses into the country 

 rocks, at the same time impregnating tliese with magmatic 

 solutions and producing marked alteration in them. 



(2) A minor fraction became separated from the main 

 magma and pursued a different course of differentiation, pro- 

 ducing complementary types in the dolerites and the red 

 aplite, as well a.i the soda aplites and soda granophyres by 

 further differentiation of the dolerite sub-magma. The 



(55) An alternative reading of the evidence would place the 

 porphyritic granite first in order of injection, carrying with it 

 small included fragments of diorite, the main mass of semi- 

 crystallized diorite being erupted through the granite very shortly 

 afterwards. With ''swirling" contacts it is diflBcult at times to 

 tell which rock came first. 



