206 WALTER HOWCHIN 
The glacial deposits vary from a stiff blue clay to sandstones. 
The clay is often gritty and carries pockets of sand and stones, 
with isolated larger stones up to 20 feet in diameter. Many of the 
included erratics are strongly glaciated (see Fig. 7). The sand- 
stones are of very unequal hardness, varying from a loose friable 
stone to a highly indurated or siliceous rock, and are often pebbly. 
Fic. 7.—Glaciated erratic of quartzite, taken from Permo-Carboniferous bowlder 
clay, in washout at Poole’s Flat, near Normanville,S. Aus. 4 natural size. W. How- 
chin, photo. 
The planes of deposition are distorted in places and the microscopic 
structure of the stone gives striking contrasts. In the same section, 
highly rounded quartz grains are mixed with angular and splintery 
quartz, and in some cases the stone is entirely composed of the 
latter. The ground mass consists of exceedingly minute fragments 
of comminuted quartz known as “‘rock-flour.”” The sandstones 
are quarried in places for road metal and building stones. The 
sandstones are mostly characteristic of the upper members of the 
series and the bowlder clays of the lower. In the extensive dis- 
