1”

ECONOMIC GEOLOGY

washing in water. The conclusive evidence against the
growth of nuggets in the gravels is their distribution. No
nuggets are found in goldfields where the gold in the lodes
is in minute particles; or they may be found, e.g. in the
Rand in South Africa, only where coarse gold has been
formed in secondary quartz-veins. In Ballarat East, as
shown in Fig. 11, the nuggets were found along a line where
nuggety patches occur in the lodes,
These patches are exposed on the
hillside ; pebbles washed down the
slope, knocked out the brittle
quartz and hammered the patch
into a nugget. This origin is consistent
 with the investigations on
nuggets of A. Liversidge (F.R. Soe.
New South Wales, xxvii, 1893, p.
343; xl, 1906, p. 161).
The mining of Ballarat East was
dependent on some clue to the
arrangement of these nuggety
patches. One having been found
where a quartz-vein met g vertical
brown line, this line was followed
and led to other patches of gold,
where it met a quartz-vein. The
ine was therefore called the indicator.
 Several of these indica-‘ors
 have been found in the slates
at Ballarat East, and have been
traced for eight miles along the
field. They vary from about onesixteenth
 to a quarter of an inch
in thickness; the main indicator
sometimes divides into three layers which have a tota] thickness
 of half an inch. Their thickness and their dark colour,
below the oxidized zone, is expressed by the names of the
Pencil Mark and the Telegraph Line given to two of them,
The microscopic structure of the indicators shows that most
of them consist of bands of chlorite developed in the slate
along planes of slipping (Fig. 12). The indicators in places
occur along the cleavage planes, but often cross them. An