GEOLOGICAL NOTES 
By A. N. LEWIS, M.C., LL.B. 
Tlie camp' site for Easter, 11)24, near 
the ‘'Narrows/’ at the entrance to 
Blackman's LSav, provided sufficient 
points of interest to occupy fully the 
time of all the members interested in 
this branch of the club’s activities. 
The East Coast of Tasmania, in con¬ 
formity with the whole eastern littoral 
of the Australian continent, has been 
given its general outline by a series -of 
great earth movements in comparatively 
recent times. Owing to an adjustment 
in the earth's interior, generally ascrib¬ 
ed to the settling towards the centre of 
rock and mineral mass having higher 
specific gravity than the average, a con¬ 
siderable sinking of the floor of the sea 
off the East Coast of Australia, accom¬ 
panied by the elevation of the mountain 
ranges further in Land, occurred during 
earlv Pleistocene times. This sinking 
drew with it portion of the coastline, 
which broke in successive lines of faults 
running parallel to the coast. Great 
blocks of land were submerged to differ¬ 
ent depths, the farthest seaward natu¬ 
rally dropping the deepest. And our 
present coast rises in step after step, now 
indicated by broken lines of hills to the 
ranges nowhere far inlan'L 
These faults seldom rim in a straight 
line, hut, as is to be expected when it 
is remembered that they are simply a 
break across a ruck mass, they present 
a ragged edge, the lines of the break 
often running at an angle of 45 degrees 
from the general line of the fault, and 
intersecting each other at various points. 
1 hir East Coast follows in succession 
linos formed this wa,v. Further varia¬ 
tion is given by the pre-fault valleys, 
which have been submerged as the coast 
fell away. Wilmot Harbour is a good 
example of this, and also it must be 
remembered that during the recent ice 
age the level of the ocean was at least 
150 feet lower than it now is. During 
that time streams wore out valleys down 
to the then sea level. As the water 
rose with the disappearance of the great 
ice sheets these valleys were flooded, or 
as the technical term goes, "drowned.’’ 
A tine cliff section is exposed between 
Cape Paul Lama non and the “Narrows/ 
and Minrtl cliffs~oceur at-tlie point.* of the 
south coast of l!lac.kman’s Bay. The 
rocks exposed on both sides of the camp 
site were the common glacial conglo¬ 
merates of the penno-earbomferous 
period. These are the results of a very 
severe ice age in the distant past, dur¬ 
ing which, it is surmised, an ice sheet 
crept up from the South Pole and 
covered Tasmania, reaching to at least 
the centre of Victoria and the vicinity 
of Adelaide, with glaciers at -Maitland, 
in New South Wales, and right up in tlie 
tropics in latitude Jo deg. S. in the north 
of West Australia. (This ice invasion, 
of course, preceded the one the effects 
of which we sec on our mountain pla¬ 
teaux by millions of years, and was not 
in any way connected with this recent 
one.) 
Wo can fell that these rock- are of 
glacial origin hv the way the component 
pebbles and boulders are distributed 
through them. A stream washes pebbles 
down its bed. but in doing so roll- them 
over and wears them smooth. When its 
flow is checked it drops the heaviest 
first, and carries the lightest far farther 
on. Thus it sorts its load. Also, as 
a stream usually cuts only through a 
limited number of kinds of rock, and as 
each kind lies a different weight, you 
usually find in streams formed conglo¬ 
merate only one size of pebble, and of 
one type of rock in one place. ft is 
very different with ice, which may 
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