209 
webs indicates its titaniferous character. All stages of alter- 
ation, from a mere peripheral zone to complete replacement 
by sagenite, occur. Tourmaline and zircon occur. (Plate 
xxxiv., fig. 4.) 
xxxv Dike RT FET Devs tri ¢ t Upper, Creta 
ceous (desert sandstone) formation. 
Macroscopic character s.—Typical porcelain- 
ized desert sandstone. Light yellowish in colour and ex- 
tremely tough, consists of rather fine, angular quartz frag- 
ments, cemented by fine, white, amorphous, opaline material. 
Very markedly conchoidal fracture. 
Microscopie characters.—Larger fragments 
are of medium size, and are angular to subangular. Nearly 
all quartz, with only a few grains of microcline. Many of 
the particles exhibit strain phenomena, whose characters in- 
dicate that they were produced before the redistribution of 
the mineral; that is, that this rock has been formed from 
the materials of an older quartz rock which had undergone 
considerable pressure. It is almost certain that the older 
rocks must have been the Cambrian felspathic quartzites. A 
few cherty fragments are present. There are a fair number 
of broken crystals of zircon, and a very few grains of tour- 
maline and magnetite. A good deal of the interstitial mate- 
rial consists of very angular quartz grains down to sub- 
microscopic dimensions. There is also a great deal of a white 
opaque substance, probably kaolin. The remainder is 
chiefly fine chalcedony, much of it showing evidence of the 
infilling of irregular cavities. In the centre of some of these 
cavities a little isotropic opal occurs, but only in very small 
quantities. There is no evidence of secondary outgrowth of 
quartz grains. (Plate xxxiv., fig. 5.) 
xxxvius AM ll ¡a me rekk 
An aboriginal chipping, picked up on the surface. From 
the great abundance of similar material in large angular 
pieces, evidently a local rock. 
Macroscopic characters. — Perfectly homo- 
geneous, structureless rock, of light greyish-yellow colour. 
Perfectly conchoidal fracture. Very tough and hard. 
Microscopie characters. — Exceedingly fine 
grained. Mostly quartzose material so exceedingly fine in 
texture as to be almost unresolvable under the microscope. 
This is very variable in translucency ; some of it is almost 
opaque, some quite transparent. It forms quite 90 per cent. 
of the bulk of the rock. The grains scattered through it, 
quite irregularly, are very sharp, angular splinters of quartz 
and an occasional zircon. This sharpness of the quartz grains 
is the most striking feature of the rock. They can have been 
N 
