13 
GEOLOGICAL NOTES 
By A. N. Lewis 
The Safety Cove lo:ality is not one 
of those wonderful geoiogen] museum:, 
which occur in many places through 
Tasmania; in fact, it is almost barren 
of features of interest. Furthermore, 
it has been reported on many times 
during the last century, and all its 
features fully described. Headers arc 
referred to brief reports contained in 
the accounts of the Field Naturalist 
Camps of 1913 and 1918. 
With the exception of the Point 
Puer Peninsula, some sandstone beds 
behind Carnarvon, and a few other 
outcrops running along the hills on the 
west of Port Arthur, and showing m 
places along the south seaboard, the 
locks of the district are the ubiquitous 
diabase, uniform and Uninteresting, 
and rendered only worthy of more than 
passing mention by tlie picturesque 
columnar structure of the southern ex¬ 
tremity of the beds The Point Puer 
Peninsula is composed of petmo-ear- 
boniferous mudstones, and gritty sand¬ 
stones, strata of the upper limits of the 
system faulted out of its natural rela¬ 
tions with the surrounding later beds 
of sandstone, and appearing now at the 
saino level as the mesozoic strata on its 
immediate west. The well-known cliffs 
stretching along the coast north and 
south from Eaglehawk Neck are of the 
same system, hut the connection has 
been either entirely destroyed by the 
later inruption of the masses of diabase 
that now form the hills from Cash's 
Lookout to Arthur’s Peak, or more 
probably lias been lifted by that diabase 
and all the overlying strata has since 
been washed away. These beds form 
bold cliffs on'the seaward side, but are 
uninteresting, geologically. A few strata 
contain characteristic speoiroens of ma¬ 
rine fossils of the period, but the ma¬ 
jority are entirely barren. 
A lav visitor to the southern end of 
Tasman’s Peninsula cannot avoid asking 
tho reason for the lluted structure of 
Cano Raoul and Cape Pillar and the 
cliffs between. The formation is the same 
as the well-known Organ Pipes on Mt. 
Wellington, but entirely different from 
the columnar structure to he observed 
at Burnie Breakwater, Table Cape, ari l 
the Giant’s Causeway in Ireland, wh en 
is basalt, with hexagonal columns. Dur¬ 
ing the permo-carboniferous system 
great beds of mudstone and. limestone 
were laid down. On top of these, dur¬ 
ing the lower mesozoic system (vide 
Twelvetrees’ classification of Tasman¬ 
ia: geological succession), the beds of 
sandstone were deposited. During the 
upper mesozoic system came one of 
those periods in the earth’s history 
dining which the forces of the fiery in¬ 
terior overcame the resistance of the 
hard, cold belt of rocks of the surface, 
or the compression of the outer belt ct 
solid rocks became loo severe for the 
cc-iq plastic interior, and huge quanti¬ 
ties or igneous matter forced its way 
into the formed beds of limestone and 
sandstone, and with unimaginable beat 
melting the older rock with which they 
came into contact, forcing their way 
through cracks and weak places, and 
working in sills through whole beds of 
rock, they formed in some places 
rounded bosses. in of hers , flat dykes, of 
that hard rock we know as diabase. 
Til the course of ages the softer sand¬ 
stones have in many places been worn 
away, until the hard diabase stands out 
a ,5 hills. From somewhere, probably 
under Mt. Arthur, n quantity of this 
rock welled up. One huge mass forced 
its way southward, tollowing tho level 
of the strata, thus obtaining the flat 
top noticeable on Cape Raoul, until, by 
the supply failing, or by its driving 
force failing on account of the mass 
cooling until it eoukl no longer melt 
its way and move further, it formed 
at its southern end a wall of diabase 
several hundred feet thick in the sand¬ 
stone. Probably a similar mass welled 
tip from somewhere under Arthur’s 
Peak. As time went on the action of 
the weather has worn away the over- 
lying sandstone, and the sea has eaten 
into the land through the comparative¬ 
ly soft sandstone until it lias reached 
the harder diabase, which now stands 
out for us to see in very much the 
same shape as it stopped when molten 
and cooled in the surrounding strata. 
The columns formed where the edge 
of the molten matter stopped and 
ceded right against the sandstone. 
This diabase never came out to the sur 
face as a volcano or lava flow. Prob¬ 
ably where Port Arthur now exists 
there was no diabase, and the water, 
having no hard rock to contend with, 
