GEOLOGICAL NOTES 
By A. N. Lewis, M.C., LL.B. 
A second visit by the Field Naturalists 1 
Club to Adventure Bay Inis given the 
geological section of the members an op¬ 
portunity to follow up many of the ob¬ 
servations made last year, an outline of 
which I had the privilege to contribute 
to the camp report of 1021, where I gave 
a general idea of the stratography of 
Adventure Bay. 
Further investigations of this branch 
of geology were carried out this Faster 
by members, and included in the observa¬ 
tions made was the locating of the beds 
of marine fossils in the lower coal mea¬ 
sures of Adventure Bay mentioned, and 
described by R. M. Johnston, but which 
we iconld not find last year. However, as 
1 summarised tlv features of the, strato¬ 
graphy of the district last year, and as 
these features have been very fully de¬ 
scribed hv the late .Mr, R. M. Johnston 
in his “Geology of Tasmania,” and a 
paper published on the geology of Adven¬ 
ture Bay in the Papers of the Royal So¬ 
ciety of Tasmania for 188(1, and as the 
geological survey will probably publish 
some further observations in the near 
future I shall coniine mv remarks m 
these notes to tin* development of the 
topography of the area. 
Here, as throughout Tasmania, the dia¬ 
base is the key to the topography. 
The Director of the geological survey, 
and Mr. Nye in his Underground Water 
Papers, have given a key to the median- 
ism of the diabase intrusions in the cen¬ 
tre of Tasmania, but their idea of a 
4000ft, vertical uplift, followed by hori¬ 
zontal intrusions on a vast scale hardly 
explains many of the diibase occurrences 
m tile south. The great question is 
this: Is the diabase ttiat forms Fluted 
Cape, for example, n laterally intruded 
sill from the great uplifting mass that 
formed Mount Wellington, or is it the 
top of a huge vertically thrusting 
mass that has not liepn pushed to the 
heights of the great masses inland? W e 
may have t heories, but the nwchinism of 
the great diabase intrusions lias yet to 
be worked out. 
However it occurred, the boundar¬ 
ies of the diabase did not extend far to 
the south-east of the present shore lin€ 
of South Bruny. Looking south from 
Cape Connella small patches of sedimen¬ 
tary rock can he seen still remaining in 
sheltered corners, just as it can be traced 
in tiny patehe; on Betsy Island. Tasman 
Island', and here and there in corners 
among the diabase cliffs of southern and 
south-eastern Tasmania. 
Evidently the intrusion of diabase 
either stopped near the present shore 
line, and for some distance to the south¬ 
east the land surface was continued by 
sandstones, or else in the uplifting of the 
present land surface by the intruding 
diabase, great blocks of sandstone were 
carried from the floor of the sea. The 
action of flic restless Southern Ocean 
has effaced most of the softer sediments, 
leaving only thin patches in sheltered 
corners. The erosion-resisting diabase 
lias fared better, and, with the sandstone 
cleared from its face by the action of 
the waves, now stands in bold headlands 
rising dOflOft. sheer from the sea. Even 
this iron wall of diabase is yielding to 
tlie resistless action of the elements. 
Manv jutting prominences show the level 
where cnee the line of cliffs stood. 1 he 
sea. by eating into cracks and lines of 
weakness, has cut great gulches into the 
cliff face, and in places has entirely isola¬ 
ted columns of rock which now stand as 
outliers or sea-worn monuments, one of 
which, rising several hundreds of feet 
from the sea's edge, beneath t'ape Oon- 
nella, closely resembles the Pillar on the 
C'ape of that name, discernible 1.1 miles 
to the easl ward. 
The original face of the diabase was 
very irregular, and doubtless many of 
the bays that indent the southern coast 
were caused merely by the sculpturing) 
of softer sandstones by the waves which 
were rebuffed when they had eaten 
through to the solid diabase. Traces of 
metamorphic rock found in_ the passage 
separating Penguin Island indicate that 
here .waves have eaten out a softer bed 
of rock and isolated the diabase island. 
