339 



by the occurrence of a pegmatite dyke 8 miles from the granite 

 headland. This is genetically related to the Cape Willoughby 

 massif, and carries gem tourmalines. With the crystallization 

 of the granite and associated dyke rocks, the igneous cycle 

 appears to have closed. 



The foregoing data admittedly are insufficient to deter- 

 mine the form of the intrusion, yet the writer ventures to place 

 it in the class of chonolite, as described by Daly and defined 

 by him as an igneous body: — (a) Injected into dislocated 

 rock of any kind stratified or not; and (b) of shape and 

 relations irregular in the sense that they are not those of a 

 true dyke, vein sheet, laccolite, bysmalite, or neck; and 

 (c) composed of magma, either passively squeezed into a 

 subterranean or orogenic chamber, or actively forcing apart 

 the country rocks. 



The chonolite type, therefore, covers a wide range of 

 intrusions whose form cannot be considered well characterized. 

 It is thought that, for the Willoughby massif, the evidences 

 of underground extension, horizontally, and the apparent 

 rapid closing of the igneous cycle are not favourable to a 

 batholitic nature. 



The relation of the Cape Willoughby Massif to other 

 South Australian Intrusions. — Kangaroo Island is separated 

 from the mainland of Jervis Peninsula by the narrow strait 

 of Backstairs Passage. The island really forms a continua- 

 tion of the Mount Lofty Range, cut across by the Backstairs 

 Passage, which is probably a block-faulted area. The exten- 

 sion of the island in a westerly direction is related to the 

 strike of the axis of Palaeozoic folding, and is perhaps 

 emphasized by the fact that the late Tertiary fault scarps 

 are developed parallel to the strike of the Palaeozoic folding. 



The structure of the Mount Lofty Ranges has been shown 

 to consist of a central geological axis of Pre-Cambrian schists 

 and intrusive rocks with a north-east-south-west strike, ( 26 ) and 

 developed, anticlinorially, a series of sediments dipping 

 easterly and westerly from this axis. These sediments on 

 the western side are only slightly altered, whilst their eastern 

 representatives are markedly metamorphosed, being repre- 

 sented by quartzites, schists, and marbles. 



(26) W. Howchin: Trans. Roy. Soc. S. Austr., vol. xxviii., 



1904, pp. 253-280. W. Howchin :. Ibid, vol. xxx., 1906, pp. 227- 



262. W. Howchin: Aus. Ass. Adv. Sci., 1907, Sect. Q, pp. 

 414-442. 



