Geulogy of Lily dale. '.i4 1 



Sittle quartz and a good deal of felspar microlites, giving extinction 

 singles from deg. for the majority, up to .'}() deg. for the rest. 

 .(Some of the former may be orthoclase.) Flow-structure is slightly 

 indicated by the general parallel arrrangenients of microlites and 

 phenocrysts. Granular green slightly altered l)i(jnte is abundant. 



Spec. grav. 2.66. 



Owing probably to the easy passage offered to water along its 

 intricate network of joint planes, the whole series has l>eeii 

 .subjected to such extensive alteration that it resembles more a 

 whitish baked shale than an igneous rock. Previous writers (R. A. 

 F. Murray (7) and V. R. Stirling (S)) have regarded it as meta- 

 morphosed Silurian. In this extremely altered condition, the 

 ielspar phenocrysts have disappeared, leaving rectangular cavities. 

 The ground mass is felsitic. but shows much granular secondary 

 .quartz, veined by strings of the same mineral. In the freshest 

 specimens the specific gravity is 2.66; in the altered type, it ig 

 2.37, a loss of nearly 11 per cent. 



The altered type of this series provides the chief road metal of the 

 •district, a use for which it is well adapted. Being rather brittle, it 

 is easily prepared, and. while providing binding material, its 

 •condition as an ultimate decomposition product tends to prohibit 

 .the formation of dust and mud. 



Chemical and Miner alogical Composition. — The chemical 

 analysis of a member of this series is given later, and is practically 

 identical with that of the preceding series (a). Silica (69.9 per 

 cent.) and alkalis (6.9 per cent.) are both high, constituting the 

 j-ock a toscanite like its predecessor. But, unlike its predecessor, 

 the ground mass is abundant. It is glassy or niicrociystalline, and 

 it contains but little orthoclase. 



Comparison of the toscanites {a and h). — The first two series, 

 then, are toscanites. In each case quartz never appeal- in pheno- 

 crysts, and only to a comparatively small extent in the ground 

 inass. But although their chemical composition is practically tlie 

 ^same, there is a fundamental mineralogical difference between 

 them, which prevents their being called facies of the same seiies. 

 This difference, which as a rule appears so plainly on comparing 

 .the hand specimens, inheres in the ground mass. In the first 

 -series (a), the ground mass is often practically holocrystalline. 

 owing to the abundance of orthoclase; in the second series (6), it is 

 •often almost non-crystalline, and orthoclase seems sparse or absent 

 •\vhile minute flakes of biotite are frequent. There can be no doubt 

 rthat this difference was due to the fact that mineralisers, chiefiv 



