BY \V. X. BENSON, W. S. DUN, AND W. R. BROWNE. 41!) 



the same magma reservoir. The majority of tlie types are normal dolerites, but 

 the collection also includes some containing albite or oligoclase, and there is a 

 single example of a teschenitic dolerite. The normal dolerites, though ditfering 

 much among themselves in te.xture, may quit* probably conform to a common 

 chemical type and may have affinities with the Werrie basalt, and the albitic rocks 

 may have resulted from albitization. The teschenite, however, stands apart from 

 the others, and its miueralogical characteristics are closer to those of the Tertiary 

 alkaline intrusives of the State than to anything of Carboniferous age with 

 which we are acquainted. However this fact is hardly sufficient in itself to 

 justify any conclusion as to the geological age of the intrusion and the field- 

 relations shed no great light on the matter. 



(a) Normal Dolerites. These comprise most of the dykes around Currabubula, 

 as well as those actually in the Warragundi complex. The rocks are all holo- 

 crystalline, with or without phenocrysts, and vary considerably in grainsize. 



Specimen 1502, cutting through the liasalt in Portions 302 and 307, is a por- 

 phyritic rock. The phenocrysts, roughly prismatic zoned crystals of basic laln-a- 

 dorite (near Abso Anro) up to 4 mm. in length, are much cracked and carbonated, 

 the cracks being often filled with what appears to be clear secondary albite. 

 There are also long streaky inclusions of devitrified glass. The felspar of the 

 groundmass is zoned acid labradorite in rather stumpy laths about .25 mm. long, 

 without any definite arrangement. Augite is plentiful in small prisms, occa- 

 sionally slightly ophitie towards the felspar. It is pale reddish-brown and faintly 

 pleoehroic. Ilmenite is almost as abundant as augite and is much leucoxenised . 

 Apatite is rare. Chlorite is interstitial but may also be associated with calcite 

 as pseudomorphs after some unknown mineral. 



A somewhat similar roek in many respects is 1527, from a dyke in Rocky 

 Creek, in Portion 287, Currabubula. The i)lagioclase phenocrysts appear slightly 

 less basic than those of 1502, and are much altered to carbonates, with inclusions 

 of what appear to be devitrified base. Slight zoning is noticed. The felspars 

 of the groundmass are andesine, about Ab-,:, An4r., about 3 mm. long and slightly 

 zoned, and there is abundant well-crystallized magnetite, with very tiny apatit« 

 needles. Ferro-magnesian minerals are reiiresented only by interstitial chhu-ite, 

 and by small amounts of carbonates. There is a small amount of interstitial prim- 

 ary quartz. 



The medium-grained rock forming the central part of a dyke in the railway 

 cutting in Portion .34, Currabubula, is a felspathic dolerite (1509). It is non- 

 porphyi'itic. The felspar, tabular-colunmar in habit, ranges in lengtli from .3 

 to 3 mm. It is strongly zoned, the variation being from bytownite to andesine. 

 Alteration is a very marked feature, the crystals being seamed with irregular veins 

 of what appears to be secondary albite. The subordinate augite, of a pale 

 greyish-brown colour, is partially idiomorjiliic and partly opliitie to the felspar. 

 It is altering to brown, strongly pleoehroic hornblende. Ilmenite is fairly plenti- 

 ful, and long apatite needles are included in the felspar. Interstitial chlorite and 

 calcite are fairly plentiful, and a zeolite, (?)' chabazite, occurs in places. 



The basic rocks in immediate association with the Warrag^undi volcanic centre 

 occur as sills and dykes intersecting the basalt, tuffs and other products of erup- 

 tion. They have not been exhaustively studied in the field and will accordingly 

 be only briefiy referred to here. The specimens that have been examined exliibit 

 many textural variations. Some of the rocks are porphwitic and a few exhibit 



