13 
GEOLOGICAL NOTES 
By W. H. Clemes, B.A., B.Sc. 
The rocks in the vicinity of Port Ar¬ 
thur are more interesting from a 
stratiographical rather than from a 
paleontological point of view, and are 
worthy of a more extended examina¬ 
tion than was possible in the limited 
time at our disposal. 
The oldest rocks in the vicinity be¬ 
long to the lower Permo-Carboniferous 
series, and comprise the usual gritty 
marine mudstones, so common in the 
'south-east of our island. They occur in 
nearly horizontal beds at Point Piter, 
and probably underlie the sandstones 
of the hills to the west of the settle¬ 
ment. The lower beds are barren argil¬ 
laceous sandstones, with iron-filled 
joints. Above occur the mudstones, and 
more or less pure limestones, containing 
the commoner Permo-Carboniferous 
marine fauna. In the middle of the beach 
at Half Moon Bay is an outcrop of 
highly metamorphic mudstone, nodu¬ 
lar iu structure, and weathered into 
curious and fantastic shapes. 
The hills to the west of Safety Cove 
are formed of Mesozoic sandstone of 
the usual type, resting conformably on 
the mudstones mentioned above. Quite 
one thousand feet of this rocJc is vis¬ 
ible, barren of all fossil remains, and 
approximating in age and texture to 
the Knoeklofty series. I understand 
that at Long Bay traces of shale are 
to he found, containing Phyllotheea and 
Zeugophyllites, ami merging into the 
coal seams of the Tasman Peninsula 
Basin. The most interesting structural 
features of the neighbourhood are duo 
to the intrusion of diabase in the later 
Mesozoic. This igneous rock-material 
has forced its way up into and between 
the beds of the other strata, forming 
the whole of the mountains to the east 
of the hay, and capping the mountains 
to the west. The flatness of the plains 
is due to the moulding of the overlying 
strata, between the layers of which it 
has forced its way. Most of the over- 
lying sedimentary rock has been worn 
away; only one small portion can be 
seen between Arthur's Peak and the 
Pillar. The rock on the whole is mas¬ 
sive in type, as at Brown Mountain, 
tut at tho edge of the sill fine ex¬ 
amples of columnar structure are 
noticeable, formed by the more rapid 
rate of cooling at that point. The col¬ 
umns of the Raoul and the Pillar are 
familiar to all, and the same structure 
may be seen right round the outer 
fringes of the coast, the massive type 
only being found further in. To the 
north of Cape Raoul, the diabase can 
be seen resting, conformably on the 
earlier sandstones. The deep Port 
Arthur bay has been formed along the 
junction between the diabase and the 
mudstones and sandstones. When the 
diabase was forced into the older strata 
at a temperature of about 2,C0Cdeg. F., 
it produced great changes in the rocks 
with which it came into contact. It 
was responsible for the metamorphism 
m the mudstones at Half-Moon Bay, 
and numerous examples of its action on 
tile sandstones could he seen, the best 
being near to the Remarkable Cave, Mr. 
Arndell Lewis has described it before, 
and I cannot do better than quote his 
words:—"In one place the following 
structure can be easily seen. There is 
a small cliff of sandstones, with con¬ 
glomerates on the top. underneath 
which can be seen the first effects of 
the enormous heating from below. For 
a foot or so. the change is hardly no¬ 
ticeable, and is confined to a hardening 
of the lock, but after that it changes 
with increasing rapidity Soon the rock 
becomes a dull brown, and very much 
1 ardor, and large specks of mica ap¬ 
pear. Very soon the rock is so hard 
as to lie unaffected by a hammer blow, 
but still preserves its stratified form. 
Up through cracks has welled thin 
sh< ets of diabase, as miniature dykes, 
telling of the sill not far below. Great 
masses of entirely changed matter aro 
seen mixed up with the other rock, 
which soon loses all resemblance to any 
stratified rock, and becomes purely a 
mass of quartzite. Tho whole rock is 
now changed in colour. Some of it is 
a pale green, some blue, other parts 
are a shining black; some again are 
like polished marble, and all of it is 
much harder than the ordinary diabase 
which comes just below it.” Consider¬ 
able deformation has also taken place 
near tho intrusion. Many caves nave 
been hollowed out iu the diabase by 
the action of tho waves, the best known 
