20 



W. N. Benson — Spilite Lavas, etc., in N.S. Wales. 



series in. the Newcastle District to the south, and Jurassic sandstone 

 lies horizontally on its denuded surface. 



Following the peridotite intrusions (with which came a minor 

 amount of eucrite-gabhro) were minor intrusions of dolerite followed 

 by a sequence of granitic intrusions that extend into the early 

 Mesozoic. (See Figure, p. 19.) 



The spilite lavas are similar to those described by ^Messrs. Dewey 

 and Flett. They are dense, tine-grained, often more or less vesicular. 

 In texture they are trachytic or pilotaxitic, with a varying amount 

 of augite and magnetite among the felspar laths. According to the 

 character of the occurrence the rock will have well-formed or skeleton 

 crystals of felspar and iron ores, less rarely is the pyroxene well- 

 formed. A partly devitrified base may be present ; more rarely the 

 rock is holocrystalline. Usually the augite is entirely chanj>e(l to 

 uralite and other products, and the felspar indeterminable through 

 clouding with sericite chlorite, epidote, etc. Where determinable 

 the felspar is invariably albite-oligoclase. The following chemical 

 analyses will serve to show the affinity with spilites of Cornwall. As 

 will be seen, this similarity descends even into such a minor point as 

 the absence of barium. 



100-26 100-63 100-25 100-18 



I. Spilite, Nundle, New South Wales (analysed by W. N. Benson). 

 II. ,, Mullion Island, Cornwall (analysed by W. Pollard). 



III. ,, Tregidden, Cornwall (analysed by E. G. Eadley). 



IV. Albite dolerite , Bingara, New South Wales (analysed by W. N. Benson) . 



The dolerites associated with the spilites are similar to those 

 occurring with spilites in other localities. While in certain rocks, 

 particularly those containing quartz, the plagioclase is andesine, in 

 others it is nearly pure albite. They are often strongly titaniferous, 

 and may contain a good deal of apatite and primary pyrites. The 

 augites are more or less uralitizc^d. 



Another point of interest in connexion with these Australian 



