118 E. 0, Teale: 



The largest felspar phenocrysts are inclined to be of rather stout 

 habit, showing somewhat broad twin lamellae, and generally low. 

 extinctions, suggesting oligoclase. 



Tha numerous felspar laths, which bulk most largely in the slide^ 

 and show simple twinning, are probably sanidine, as also are a 

 number of definitely prismatic forms of intermediate size. Mag- 

 netite is abundant, but almost all trace of the original ferro-mag- 

 nesian mineral has disappeared. Veins and patches of secondary- 

 quartz and chlorite are present, and one portion of the slide has 

 been almost completely silicified, showing the quartz both as a 

 mosaic and microcrystalline form stained by patches of hematite- 

 and some chlorite. 



The rock appears to represent an interesting type of altered- 

 trachyte or trachytic andesite. 



No. 14 is a dark grey, finely porphyritic rock macroscopically, 

 but the thin section shows a distinct fragmental structure, with- 

 abundant angular fragments of triclinic felspar (probably am 

 albite of the type Abjg Anj). Smaller felspar laths are present, 

 some of which are triclinic, with Ioav extinctions, and, maybe, oligo- 

 clase, also magnetite and fragments of altered rocks similar to 12;. 

 much chloritized. The base is finely granular in part, due to second- 

 ary silicification. There are no recognisable original ferro-mag- 

 nesian minerals, but chlorite is abundant. The rock probably re- 

 presents an altered andesitic ash. 



Acid Porphyritic and Pyroclastic Rocks. — Rocks of this type^ 

 are very abundant, and show considerable variety of colour and 

 texture. In general a prevailing red to brown colour is most com- 

 mon, but various shades of green to grey are also found. 



Flow structure is not common, and was only noted in one place, 

 namely, in the ridge between Ti-Tree Creek and Yellow Water Holes^ 

 Creek, and W.N.W. from Beecher's. 



Quartz and felspar either as fragments or phenocrysts are usually 

 apparent macroscopically, and in tliin sections the rocks of this- 

 division can generally ba readily separated into two groups — 



(1) Those definitely fragmental, representing altered pyro- 

 clastic material. 

 (2) Those cif the more normal quartz-porphyrite type, probably" 

 partly hypabassal, having solidified in the fissures, or 

 vents, through which the more superficial material' 

 readied the ' surface. 



Both these types are well represented along the Tara Range. 



