(.'col <,;/,/ ,,J Lilii<hih'.. 839 



tion, and j)()luris;it ion iharattors of hyj)i'rstheiiL'. Iron oxide, 

 apatite, and zitcoiis (uciir as accessories. 'J'lie ground mass is 

 like that of the l)asal inendjer, except that the orthoclase is not 

 idioniorphic, but allotrioniorphic. It envelopes the laths of plagio- 

 clase, and occupies the interstitial spaces so continuously that 

 there is but little glassy base present. As the orthoclase has 

 crystallised from various centres, it produces an extinction effect 

 resembling strain shadows. Pronounced tluxional arrangement of 

 laths and phenocrysts occurs. Granular chlorite and biotite are 

 present, and also a little quartz. 



The spec. grav. is 2.6'2 (for least altered specimens). 



It forms the surface rock of the chief part of Lilydale, and also 

 constitutes a big part of the hills, -which overlook the town on the 

 north-east. 



3. Upper Member. — Specimen from Allot. 24, .south end. A 

 gray slate-coloured rock, fine grained, hard and tough, showing 

 felspar phenocrysts with fluxion al arrangement. Idiomorphic 

 phenocrysts of plagioclase (probably labradorite) are common ; 

 apatite, zircon, and iron oxide rather frequent. The ground mass 

 is like that of the middle member, and consists of microlites (prob- 

 ably oligoclase), surrounded by optically continuous patches of 

 orthoclase. Elongated streaky areas of sericitic material abundant, 

 and this, together with secondary quartz, occupies what seem to 1)8 

 original vesicles, or planes of weakness. 



Spec. grav. 2.65. 



Chemical and Mineralogical Characteristics. — The three members 

 of the series agree in the relatively small amount of primary 

 quartz present, considering the high SiOo contents (68 per cent.), 

 and also in the prevalence of orthoclase in the ground mass, account- 

 ing for- the high alkali contents (6.98 per cent.). They differ 

 chiefly in the structure of the ground mass. In the basal member, 

 the orthoclase formed regular-shaped crystals, and these set in a 

 cryptocrystalline base, give the rock its brittle character. In the 

 other mem])eis, the orthoclase crystallised more extensively, the 

 patches from various centres moulding themselves on one another, 

 and occupying the interstitial spaces so fully that but little base 

 remains. These rocks are therefore very tough. 



The abundance of orthoclase, and the subordinate quantity of 

 quartz, in the ground mass of this series, has been effected by the 

 assistance of mineralisers. especially water, of whose plentiful 

 supply the vesicles bear evidence. This is further discussed below. 



