210 
subjected to no attrition whatever, or, small as they are, they 
would have had the extremely sharp edges rounded off. The 
section, as a whole, shows very marked evidence of flow 
structure, quite like that so often seen in a rhyolite. 16 has 
evidently been caused to flow while in a plastic condition. 
There is no sufficient evidence upon which to ground the 
suggestion that this rock has had a glacial origin, but, con- 
sidering its very peculiar structure and the great abundance 
and variety and large size of the erratics found throughout 
the desert sandstone of the Far North, the possibility of such 
an origin is well worthy of further investigation. 
SUMMARY. 
Though the rocks which have been examined embrace 
only an exceedingly smail proportion of the quartzites and 
sandstones of the State, they form a fairly representative col- 
lection, and certain fairly reliable conclusions may be drawn 
from the descriptions: — 
1. The massive quartzites of the Mitcham formation (lying 
immediately under the Sturt glacial bed), in all their occur- 
rences from Adelaide to Mount Remarkable, are characterised 
by abundance and variety of felspar, such as is shown by no 
rock beyond the limits of this formation. 
2. The erratics from the glacial bed are certainly not frag- 
ments of Mitcham-Burnside quartzites, but somewhat re- 
semble those from the Clarendon tunnel. 
3. The quartzites associated with the archzocyathine bed 
(those of Sellick’s ТІП and Wilson) constitute another very 
definite type, quite distinct from those of Mitcham and 
Burnside. 
4. The quartzites of the Mount Barker district are dis- 
tinct from either of the abovc series. 
5. The rock from King's Bluff, Olary, shows far more re- 
semblance to those from Mount Barker than to those from 
near Adelaide. 
6. The boulders in the Inman Valley conglomerate are 
very markedly different in character from the erratics in the 
glacial bed at Blackwood. 
In conclusion, I wish to express my thanks to my frieni 
and colleague, Mr. Howchin, for the keen interest he has 
taken in the work. Many of the types which have come 
under examination are from his private collection, the con- 
tents of which he placed unreservedly at my disposal. 
I hope that the very incompleteness of the foregoing de- 
scriptions will cause some other worker to enter this field of 
investigation. I am sure that the interest of the work and 
the value of the results obtained will well compensate any 
one for the labour involved. 
