Auriferous Quartz-veins . 
117 
In the Lower Silurian rocks, the general features are the same 
throughout, though each district exhibits special peculiarities. 
The lodes or veins of quartz, from the thickness of a knife-blade 
to that of scores of feet, traverse the rocks, usually in directions 
coinciding with the strike of the uptilted strata, but sometimes 
crossing it horizontally, obliquely, or vertically. They exhibit 
the same variations as do other mineral lodes, swelling alter- 
nately into thick masses and dwindling to mere threads, or 
disappearing entirely either in a vertical or horizontal direction, 
holding even undisturbed courses for long distances, or broken 
and displaced by faults or slides, forming “saddle reefs,” as in 
the Sandhurst district, and dipping to the north or south in their 
lines of strike; or ilat reefs, as at StawelJ, and holding courses 
independent of the strike and cleavage of the containing rocks. 
In the Upper Silurian rocks some reefs occur similarly to those 
in the Lower Silurian, but they are, as before stated, very fre- 
quently associated with diorite dykes, in or with which they occur 
in every conceivable variety of form — as well-defined lodes, 
accompanying the dykes on cither wall, or intersecting them in 
directions parallel with their courses ; as vertical to nearly 
horizontal veins crossing the dykes from side to side, but not 
extending into the Silurian rock, or only to short distances; and 
as irregular strings, veins, and bunches. 
Throughout both Lower and Upper Silurian areas the aurifer- 
ous reefs, whether traversing the rocks themselves or the intrusive 
diorite dykes, occur in long belts conforming generally in direction 
to the strike of the Silurian strata. 
Within each belt are a greater or less number of different lines 
of quartz reef, and between the belts are varying widths of country 
in which little or no gold can be found, though the rocks are of 
the same character, and the quartz reefs as numerous as in the 
auriferous areas. 
Certain portions of the belts are richer than others, and intervals 
or breaks occur along them, where they appear to be lion-aurifer- 
ous; but when the different proved auriferous portions are marked 
on a map, their occurrence within tolerably well-defined parallels 
becomes very noticeable, and affords numerous suggestions for 
further exploration in search of both quartz and alluvial gold- 
workings. 
The auriferous bolts are, as far as been proved, narrower, 
and further apart, and the lines of quartz reef fewer in number, 
and, as a rule, smaller in size, in the Upper than in the Lower 
Silurian rocks; but, on the other hand, the average yield of gold 
per ton of quartz from the former has hitherto considerably ex- 
ceeded that from the latter. 
Another circumstance may here be noted, namely, that all the 
largest nuggets obtained in alluvial workings have been found 
where Lower Silurian rocks prevail. I am not aware of any 
