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The Port Victor Granite.* 



By H. W. Gartrell. 



[Communicated by W. G, Woolnough, B.Sc, F.G.S.] 



[Read October 27, 1903.] 



The granite outcrops at Port Elliot, Port Victor, and Rosetta 

 Head form a part of the northern edge of the extensive granitoid 

 belt which follows the eastern side of the Mount Lofty Ranges, 

 and skirts the southern side of Kangaroo Island. The granite is 

 intrusive, and is seen at the places mentioned and elsewhere to 

 penetrate mica schists or other highly metamorphosed rocks. 



The rocks in question possess considerable interest in their 

 comparative study with other outcrops in this vast granitic area 

 as well as from the light they may throw on the lines of distri- 

 bution which have been followed by the glacial erratics of the 

 older and newer glacial periods of South Australia. 



This paper contains the results of a careful examination of the 

 large porphyritic felspars of the rock. 



Preparation of the Material. 



Crystals were broken from the rock and freed from adherent 

 quartz. These were then broken into small fragments in a steel 

 die. All flakes of mica and fine dust were rejected and the 

 fragments each carefully examined to eliminate any fragments of 

 quartz. Large fragments were further broken to prevent inclu- 

 sions of mica and no fragments accepted with a greater dimension 

 than one-eighth of an inch. The granules were then pulverised in 

 the steel die and the powder finely ground in an agate mortar. 

 The powder was used in an air dried condition. 



Chemical Analysis of the Felspar. 



At first -75 gramme was taken for the determination of silica 

 and bases in anticipation of small quantities of lime and magnesia, 

 but this was found unwieldy and about -5 gramme taken. The 

 fused mass showed a faint greenish tinge due to a trace of 

 manganese. The silica was then estimated by the method recom- 

 mended by Hillebrand, i.e. evaporating to dryness, filtering and 



* A.n Abridged Reprint of the Essay which obtained the Tate Memorial 

 Medal, 1903. 



