338 Morris Morris: 



I'etrological Characters. — In the field, the members of this serie* 

 appear so heterogeneous as to seem capable of further subdivision. 

 But the microscopic evidence shows that they belong to one family. 

 They agree in bearing phenocrysts of felspar, and a ground mass full 

 of orthoclase, but with relatively little (juart/. They differ in. 

 the structure of the ground mass, and in the nature and amount 

 of ferro-magnesian minei-als present. 



Three types have been selected for description, (1) from the base 

 of the series, (2) from the middle (3) from the top. 



1. The Basal Member. — Specimen from quarry, allot. 24, north 

 end. A hard, brittle, bluish-gray streaky rock, fine grained, with 

 occasional phenocrysts of felspar. 



Under the miscroscope, it is found that idiomorphic phenocrysta 

 of plagioclase (probably oligoclase) are sparingly developed, and 

 arranged parallel to the flow structures of the ground mass, which 

 consists chiefly of felspar miciolites. set in a sparse cryptocrystal- 

 line matrix. These microlites are of two kinds — (a) very minute 

 laths of plagioclase (probably oligoclase), (b) larger and rhombic 

 or square-shaped crystals of orthoclase. Orthoclase is greatly in 

 excess of plagioclase in the ground mass, and apparently of the 

 phenocrysts also. This is due to the high percentage of alkalis 

 present (viz., 6.98 per cent.). Of CaO there is 1.95 per cent., most 

 of which has combined with COg without being removed, This- 

 is clear from the presence of 1.80 per cent, of CaO in the next 

 series (6), which is nearly identical in chemical composition, and 

 containa no CO5. Iron oxide in the rectangular grains occur spar- 

 ingly. Sericitic material and some secondary quartz leached from 

 the matrix, occupy original vesicles or planes of weakness, and give 

 the rock a .streaky appearance. The specific gravity of this rock is 

 2.489. The chemical analysis is given later. 



Its industrial value as metal for roads and ballasts is due to its 

 hardness, to its brittleness rendering it easy of preparation, and 

 to the absence of unstable mincials. It is ('xtfiisivcly quarried for 

 this purpose. 



2. The Middle Member. — Specimen from railway cutting behind 

 Lilydale. Like the basal member, except that it is not brittle, but, 

 on the contrary, exceedingly tough, and also much more vesicular 

 and streaky. 



Phenocrysts of plagioclase. ortlioclase (sul)ordinate), and biotite 

 in large flakes, are present, the latter being much decomposed, and 

 the alteration products fill the original steam pores. One small 

 phenocryst was found with the colour, pleochroism. cleavage, extinc- 



