602 THE GEOLOGY OF THE WARRUMBUNGLE MOUNTAINS, 



4. Name : Pilotaxitic ^girine Trachy-Andesite. Magmatic 

 name, Monzonose (see Analysis "W. 1). 



Note : this specimen is the same as W.l, which was analysed. 

 The analysis of W.l represents the composition of most of the 

 great flows of trach3^-andesite lava and phonolitic trachyte which 

 followed the outbursts of true trachyte and phonolite. In these 

 flows the iron, lime, and magnesia are higher, and the silica 

 lower than in the trachytes. However, their high percentages 

 of alkali and AlgOg show their definite relationship to the other 

 rocks. The trachy-andesites were tested for felspathoids with 

 acid and staining reagents. Rocks of similar appearance from 

 different parts of the Warrumbungles were sectioned and tested. 

 Most resisted the reagents, but a few stained slightly in the 

 ground-mass, and sometimes small nephiiinitoid crystals took the 

 stain. It appears therefore that most of these rocks are free 

 from felspathoid mineral, but some contain a little interstitial 

 nepheline. On account of their close resemblance to one another 

 in physical, mineralogical and chemical characters and their close 

 field-relationship, I have classed these rocks together as trachy- 

 andesites and phonolitic trachytes. 



W.l 27. Loc: ridge between Berum Buckle and Belar Creek, 

 about one mile N.E. of Berum Buckle. 



1. Handspecimen not unlike Gib Syenite. It abounds in 

 vesicles (miarolitic structure). 



2. Texture holocrystalline, uneven-grained, porphyritic with 

 trachytic fabric in the groundmass. 



3. Composition : the essential constituent is orthoclase of pris- 

 matic and acicular habit (giving lath-shaped sections). The 

 other minerals present are phenocrysts of magnetite, needles of 

 segirine, irregular grains of soda-amphibole and ferrite with iron- 

 bearing decomposition-products. 



4. Name : Porphyritic Soda-Trachyte. 



W.l 35. Loc: same as W.l 27. This rock is similar in every 

 respect to the preceding. 



