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earth's
crust. The general lines of the corrugation of the slate and sandstone
. rock layers in Stawell are accordingly very much as through the
mountains. The strike of the arches and lode lines is a little more to
the west than noticed further east, but the dip of the rock layers is,
as usual, to the south-west at an angle of about 45°. The lode
structure is simple and very uniform, being the result of a cracking
brought about by a slight longitudinal twist strain, acting with an
upward thrust. Thus, the lodes themselves bear more of the saddle
feature than do the lodes further east in these mountains, although
the same class of strain was active to a greater or less degree in the
creation of lode receptacles throughout the whole area of the latter.
Here, the lodes ride the arches of the corrugated strata somewhat after
the fashion in Bendigo, with this difference, however, that the whole
corrugation of the field has received a greater side squeezing; so much
so, indeed, that the crowns of the arches bear much the same relation
to the arch sides as does the curve of a hairpin to its forks, while
the strata at Bendigo have been corrugated more after the fashion of
ordinary roofing iron. Here the arches lean to the north-east, and the
main system of lodes—a system on which all the mining in Stawell to
date has been confined—rides one main arch and sends its legs down, as
so-called verticals, to great depths on either side of it. The strike
of these legs, though almost, is not exactly, parallel to the strike of
the strata, and as a consequence, perhaps, of an upward thrust to the
field, fin-like, rather than wing-like, cracks were formed, running
from one leg to the other. It was the outcrop of one of these fin-like
occurrences of quartz—these so-called " flat reefs "—that first
received attention from miners, and when it was followed to the point
of its junction with the western leg of the saddle, the leg itself
received the name of the Cross lleef, because its course proved to be
across that of its fin-like associate. These arbitrary terms are very
misleading to outsiders. One naturally thinks when the term " cross
reef " is used, that the actual cross reef is referred to. The term "
cross reef," however, is the name of the western leg of the main lode
system.
These
legs, known as verticals, go to great depths, and probably lose their
identity in the cracks of the inverted arches of the corrugated strata.
From the nature of their structure, and the latter's association with
the general corrugation of the field, it is reasonable to suppose that
other arch occurrences of quartz, having similar legs, remain to be
found at lower depths slightly to the west of the opened formations.
Much
dyke material is associated with the Stawell lodes. In places it is
coarse-grained, and in one of the mullock heaps, near a deep shaft, I
found dyke material very like basalt.
As
mentioned, the strike of the strata and the lodes of Stawell runs
almost north-west and south-east. The sedimentary rock feathers out on
the granite a mile or so to the west, and there are evidences on all
sides
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