no 



Olary. — Behind Olary and near King's Bluff is a series 

 of granite rocks discovered by Mr. Howchin and described 

 by Dr. Woolnough.^i'^) They are very gneissic in appearance 

 and shattered in microscopical section. Their two chief dis- 

 tinguishing characteristics are (a) acidity of the plagioclases 

 and (h) presence of much titanium. These two featui'es are 

 among the most noteworthy of the Houghton rocks. An un- 

 usual form of aplite, containing large crystals of titaniferous 

 iron, I found in a creek about half a mile to the north of 

 King's Bluff, and is described in the petrological portion of 

 this paper. 



At Radium Hill, near Olary, Mr. Mawson (n) has found 

 the highly-titaniferous mineral davidite, in a pegmatite vein 

 intruding Pre-Cambrian quartzite, and containing other titan- 

 iferous iron minerals, with vanadium mica and qiiartz. 



Jameatown. — In the collection of the Sydney University 

 is a boulder found in the Cambrian till at Jamestown. It 

 is a quartzose felspar porphyry, which on microscopical exam- 

 ination is closely related to the Houghton magma rocks, and 

 must be regarded as an effusive prodiict of that magma. 



These instances far removed from Adelaide of rocks 

 similar to the Houghton rocks show the probability of 

 the wide extent of the Houghton magma. Though they may 

 not all be of Pre-Cambrian age, it does not affect their co- 

 relation, for even in the Mount Lofty Ranges it is by no 

 means certain that the titaniferous products of this magma 

 are Pre-Cambrian. (12) 



PART II. 



Petbogeaphical Descriptions of the Pre-Cambrian 

 Rocks. 



a. the igneous rocks. 



i. Inglewood District. 

 As conveying a better general idea of the intrusive mass 

 in the Inglewood district, it has been thought advisable to 

 describe collectively the mineralogical and structural features 

 noted in the examination of a large number of slides before 

 attempting the descriptions of the rock types. 



a. Mineralogical Featiires. 



On account of their predominance the group of felspars 

 is treated first. 



(10) Trans. Roy. Soc, S.A., xxviii.. 1904, p. 181 et seq. 



(ai) Trans. Roy. Soc, S.A., 1906, p. 188. 



^12) W. Howchin, Trans. Roy. Soc, S.A., xxx., 1906, p. 254. 



