GEOLOGICAL NOTES 
By A. N. LEWIS, M.C., LL.M. 
Although Safety Cove, I’ort Arthur, 
iloe.s not provide many features of inter¬ 
est, several formations can be studieil 
i’ere Itetter than in most idaces, notably 
Iht contact of the dolerite (diabiuse) with 
tlie sandstone near Itcmarkalile Cave. 
rermo-carltoniferous mudstones occur 
at I’oint rttcr tind make up tlie well- 
known “Suicide Cliffs." They contain 
a few tyiilcal fos.sil.s, and are evidentiy 
members of the Upper Marine Series. 
I'-rom .several miles north of Port Ar¬ 
thur to the coa.st the rocks consitrt of 
Ko.ss .sand.stone.s. with occasional traces 
of fos.sil plant.s. and they merse Into 
the Ta.tman I’eninsttlar coal measures 
between Fort .trthur and Taranna. 
Dolerite outcrops on the ridgres east 
and we.st of Port .Vrthur and e.\ten i!i 
to the south In the form of massive 
stils. Tlte.se silts—Cape Raoul jind Tas¬ 
man Island form tyidcal examides—arc 
obviously lateral exten.sions of the main 
muss further north. On the edge of 
the sills the mechanictsnt of the in¬ 
trusion can he studied with Kfeat ease. 
c.nd particularly in the vicinity of the 
P.emarktiltle Cave many fine verticai 
and horizontal .secttoits are to lie seen. 
The dolerite. welling tt|iwaril in the 
form probably of a massive dyke some¬ 
where in the vicinity of Mount Arthur, 
has exteiidcfl laterally Ihrottgh the s.tnd- 
stones by sloping and absorbing block 
of the older rock. In this vicinity yott 
can see every stage from thin faces of 
•lo'erito beginning to merge their way 
tbioitgh cracks or weak lines of .strata 
an.I through more mas.sive examitles of 
the .same features to the stage where 
several of these faces and small sills 
jolt., and gradually .ah.sorb large blocc-; 
of .sandstone Isolated in this way. and 
Tight at the Remarkable Cave some 
small mas.ses of .sandstone—inclusions 
if a very eonsideraltle body of dolerite—. 
•■ati he .seen. Nowhere is it clearer .that 
the dolerite intruded without any 
violenee. 
Coast features have been largely lus). 
diiced by erosion of the softer sand¬ 
stones from the.se dolerite sills, leaving 
southward exten.sions in the form of 
capes, sueh its Cape Raoul. On Tasman 
Island there is a tiny patch of sand¬ 
stone, it small remnant of the rock that 
once clotheti the whole .south cotist o£ 
the penin.sul: ami ti.sually .small patches 
arc to l»e .seen here and there. The main 
coast line hits been mainly itroduced by 
hit.' Tertiary block faulting, and the 
trend of the.“e fuult.s can be followed 
bje oltserving the .series of .straight line.s 
which make up the coa.st of thi.s part 
of Tasmania. The .shallow' water that 
extends for .some 15 miles south of Ta.s- 
mtip's Peninsula evidently covers a 
further portion of what was once part 
of the iieniiisula. and has been sub¬ 
merged by Ibis faulting. The iiresencc' 
of the Point Piter limestones is another 
pi oof of faulting i)roce.sse.s. 
Sand dime's and the way they are 
formed c;in he studied .to great advant- 
ar.c here. It Is Piirliciilarly noticeabla 
liiut where the beach is subject to the 
fullest force of the wind high dunes 
do not accumulate, their tojis being 
bl.iwn off and dustriubuted across the 
back country. Rut where, as in Ualf- 
Monn Ray. the beach Is somewhat shell- 
l ied from the full blast of the wiml, they 
accumulate to a great height. On the 
olhet hand, in still more sheltered 
loctilities. such as Safety Cove, there is 
not sufllcient power In the wind to pro- 
lUico sand dunes of any height. The, 
country between Remarkable Cave and 
Safety Cove is covered with wimi-blown, 
sand, the product of the erosion of the 
South Coast. 
