203 
certain bands ground mass is absent and the quartz frag- 
ments are cemented by secondary outgrowth of the original 
grains. 'The rock has undergone very considerable pressure. 
Where there is no fine-grained cement undulose extinction is 
very strongly developed, but where there is a cement between 
the grains this phenomenon is not observed. "Throughout 
the whole rock a very marked parallel structure has been de- 
developed. This is expressed by a series of parallel planes 
crowded with minute liquid and gas cavities. "These planes 
are interrupted where they pass from a grain into the base, 
but re-appear in the same direction in the next original 
grain. The liquid cavities contain minute bubbles, but in 
no instance could I detect spontaneous movement. (Plate 
zu, NED): 
xix. Mount Lofty. Quarry in the northern peak of 
Mount Lofty. 
Macroscopic characters.—Anintensely white, 
moderately coarse-grained rock with granular fracture. No 
constituents other than quartz can be made out. Its general 
appearance is very well described by its local name of “Sugar- 
loaf Rock." 
Macroscopic character s.—Texture medium, 
structure distinctly foliated. Consists essentially of quartz 
and muscovite, the latter chiefly of the sericitic variety. A 
notable feature is the entire absence of felspar of any kind. 
Crushing has been very intense, so that the original quartz 
grains have been completely shattered. All the particles in 
the rock are extremely angular and show shadowy extinction. 
In some instances the quartz granules are in optical contact, 
but generally are separated by at least a film of sericite. In 
the interstices betwesn the quartz grains there are consider- 
able areas occupied by a very fine-grained aggregate of 
sericite and some quartz. A comparatively few large flakes 
of muscovite also occur. The rock may originally have con- 
tained some felspar, which was subsequently sericitized ; this 
is improbable, as there is no trace whatever of original fel- 
spar. 
zo орар edm Sturd: 
Macroscopic characters. —Fine saccharoidal 
quartzite, somewhat fimer in grain than xix. and slightly 
pinkish in parts. А little muscovite is visible. Fracture is 
conchoidal and lustre vitreous. 
Microscopic character s.—Texture medium, 
but somewhat variable, structure markedly schistose. Prac- 
tically a pure quartz rock. The grains are extremely angu- 
lar, and show the effects of intense crush in optical anomaly 
and complete shattering. Some of the particles show evi- 
