The
Maldon gold-field is situated on country having an elevation above
sea-level of about 1,200 feet, and it was opened first (then known as
the New Porcupine) in the " early fifties" by diggers in search of
wash-dirt gold. Its rocks are composed of slate and sandstone layers,
similar to most of the gold-fields of this State. This material is of
sedimentary origin, and it was brought in from lands of the past when
the Maldon area was under the ocean. Its layers have been crumpled in
the form of corrugated iron, such as we might imagine a sheet of
ordinary corrugated iron would be if compressed to half its ordinary
width. The corrugation thus produced has the lines of its arches
running about 10° west of north, and these arches lean to the west at
an angle from the vertical of about 45°. In other words, the " underlay
" of the rock beds is to the east, although its amount varies, the
south-eastern part being more nearly vertical than 45°, and some parts
of the north-western part of the field showing a flatter "underlay."
Taking the original thickness of this corrugated mass of sedimentary
rock at 3 miles, fully three-fourths of it appears to have been removed
by the wear of ages. As a mantle formed of horizontal sheets of
sediments, it received rough treatment from the slow moving waves of
granite beneath it.
The
granite which caused the alteration of the sedimentary rocks of Maldon
is to be seen in outcrop to the east, north, and west of the town. This
outcrop is in the form of a crescent, the bow to the north. The
sedimentary rocks have been subject to such great heat that, speaking
generally, their nature has been altered, as clay is turned into brick.
The heat not only made its presence felt in the layers of sedimentary
rock immediately in contact with the granite, but also in the numerous
lines of breakage in them, up which jets of fluid materials from the
granite appear to have been forced. These jets, now solidified, we know
as dykes. Afterwards, when the rocks had cooled sufficiently, they
became permeated with minerals associated with sulphur. As the country
was elevated and the wear of the surface went on, and the region became
cooler, the rock beds became crisp enough to allow of their being
fractured. These fractures were started when the corrugation of the
rock beds took place.
In
addition to the main crack systems formed in the corrugated mass of
sediments, thousands of other smaller cracks in the mass were formed.
These were due to the general shrinkage of the rock masses, following a
lowering of temperature. This shrinkage widened and made more definite
the main systems of cracks, which ran in almost parallel lines north
and south along, and in, the corrugated mass of the field. When the
temperature was sufficiently
[Report sent in 1st September, 1903.]
A 2
