137 



iwell marked, the rock being made up of parallel small flakes 

 'of iron-ore, with black to reddish-black metallic lustre, and 

 ■deep-yellow-brown, or quite opaque when examined by trans- 

 mitted light. It contains a very little quartz in small angular 

 grains. Chemically examined, it is found to be soluble to 

 some extent in hydrochloric acid, and upon addition of tin to 

 the solution the violet colour shows the presence of titanium. 

 There seems to be little reason to regard this rock as other 

 than a sediment, such intercalations of schistose iron-ores 

 being not infrequent in areas of ancient and metamorphosed 

 sedimentary rocks. 



Conclusion. 



Below the lower Cambrian series in the Mount Lofty 

 Ranges there lies unconformably a complex of schists and 

 gneisses. In the several localities in which they have been 

 examined they present varying degrees of metamorphism, 

 ranging from sericite schists to augen gneisses ; but on struc- 

 tural feature and mineralogical composition they appear to 

 be all members of a single sedimentary series. In Houghton 

 district other types of schist are also developed, not- 

 • ably an altered impure limestone. The evidence is insuffi- 

 'cient for determination of their age by correlation with any 

 •of the Pre-Cambrian systems adopted outside Australia. They 

 are generally insufficiently altered to place them in the Pre- 

 Algonkian division. 



Dr. Woolnough has suggested the very convenietit name 

 "Barossian" for the South Australian Pre-Cambrian series, 

 and these rocks here described, being so closely related to 

 the augen gneiss of Barossa, may fairly be held to be in- 

 cluded in that series. 



Intruding these, and typically developed in the Hough- 

 ton district, though also at Aldgate, Yankalilla, and Nor- 

 manville, is a series of igneous rocks, to which, on account 

 of their felspathic nature, the term syenite would be applied 

 by a user of the field classifications of the American authors. 

 On microscopical investigation, however, the rocks are found 

 to vary considerably in the relative quantities of their con- 

 tained felspar. Usiially plagioclase predominates, giving a 

 diorite ; while less commonly the orthoclase is predominant, 

 giving syenite. Granites and granodiorites also occur. 



The characteristic features of these intrusions are their 

 richness in titanium as ilmenite or sphene, the acidity of 

 the plagioclases, and the presence of diopside (now uralite). 

 This gives rise to most unusual rock types, e.g., ilmenite- 

 diopside-diorites, ilmenite-sphene-actinolite pegmatites, ilmen- 

 ite-felspar quartz pegmatites, and ilmenite quartz veins. 

 'Other localities further afield present rocks with some affini- 



