BY H. I. JENSEN. 879 



analcite in fair abundance, a fact which may be an indication 

 that even then there was a tendency for this to be a sodic 

 province. 



N.62. Loc: hill at junction of Manilla and Narrahri roads, 

 3^ miles north of Boggabri. Age uncertain. (Plate 1., tig.l). 



Handspecimen a dark green to black rock, showing fluxion 

 structure and perlitic cracks. A few vesicles and idiomorphic 

 phenocrysts of orthoclase, oligoclase and albite occur in it. This 

 rock occurs in the form of a narrow dyke at the foot of the hill 

 mentioned, which consists essentially of rhyolite and rhyolitic 

 tuff. 



Microscopic appearance : texture hypohyaline, porphyritic, 

 with perlitic structure in the glassy base. 



Constituents : the base which forms the bulk of the rock con- 

 sists of a greenish glass showing beautiful perlitic cracks and 

 groups of globulites. Scattered about in some abundance we 

 find beautiful idiomorphic phenocrysts of felspar, some of which 

 increase in basicity from the interior outwards. Often the core 

 is orthoclase, an intermediate zone anorthoclase, and the outer 

 zone albite or oligoclase. Neither in mineral composition nor in 

 chemical composition does this rock show decided resemblance to 

 the alkaline rocks of the Nandewars, yet it is not very distantly 

 removed from them. 



Name : Perlitic Pitchstone. Magmatic name, Riesenose (see 

 Tables i. and ii.). 



Note. — This rock is associated with holocrystalline, hemicrys- 

 talline and cr3^ptocrystalline rhvolites. 



N.67. Loc: The Pinnacles; Maule's Creek. Age: Carboniferous. 



Handspecimen a reddish conglomerate-like rock with both 

 the rounded pebbles and the finer matrix consisting of rhyolitic 

 material. 



In section the pebbles were seen to consist of a normal rhyolite 

 (qnartz, orthoclase and a little chlorite) and to have been rounded 

 by the action of water. The matrix consists of fragmentary 

 grains of quartz and felspar and volcanic ash consisting of the 



