592 THK GEOLOGY OF TlIK WAllRUMHUNGLE MOUNTAINS, 



have a core of sanidinc and a rim of albite. Next in point of 

 amount is the glassy base in which the felspars lie. It has a 

 greenish colour, and has partly devitritied into a doubly refract- 

 ing substance, probably a chloritoid. This glass probably has 

 the composition of ajgirine-augite. Soda-amphibole is present in 

 minute, highly pleochroic, blue-black and green fragments, too 

 small and ragged for exact determination. 



4. Order of consolidation : the felspar had almost finished to 

 crystallise out before the ferriferous minerals commenced to 

 crystallise. 



5. Name: Hypohyaline and orthophyric ^'Anorfhoclase-Arfved- 

 sonite Trachyte " near Orthophyre. 



W.45. Loc: Scabby Rock. 



This rock resembles W.215, both in megascopic and microscopic 

 characters. The main difference between them lies in the relative 

 proportions of glass and arfvedsonite. In W.45 the soda-amphi- 

 bole greatl}' exceeds the glass in amount. This rock has therefore 

 crystallised more slowly than AV."J15. 



W.50. Loc: Scabby Rock. 



1. Handspecimen : this rock has a grey colour; it is uneven- 

 grained, and is readily seen to consist of heterogeneous materials. 



2. Microscopic texture typical of a pyroclastic rock, tufi' or 

 breccia. 



3. Composition : the main constituent is glass in peculiar 

 boomerang-shaped and dumb-bell-shaped needles. Imbedded 

 in the meshes of this glassy matrix lie fragments of quartz, 

 probably derived from the surrounding sandstones, and also 

 fragments of magnetite, felspar, and soda-amphibole crystals. 

 The structure and nature of the constituents prove the rock to 

 be a tuff. 



4. Name : Hypohyaline Soda-trachyte Tuff. 



W.39. Loc: Timor Rock, near the " Bottle Rock." 

 1. Handspecimen dark greenish-grey in colour, and rather fine- 

 ijrained. 



