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Geology and Physical Geography: 
CHAPTER XII. 
Auriferous Quartz-veins in Lower and Upper Silurian, 
rocks . — Auriferous belts . Modes of occurrence of Gold . 
Other Minerals . Theories as to the formation of Quartz- 
veins . Nuggets . Auriferous character of Lodes at great 
depths . 
Auriferous Quartz-veins. 
In tbe preceding portion of this work no notice lias been given 
to the auriferous veins, lodes, or reefs of quartz which form so 
significant a feature in the geology of the Silurian rocks, and 
which now, and will for a long time to come, exercise so impor- 
tant a practical bearing on the prosperity of Victoria. Remarks 
on this subject have been purposely deferred to the concluding 
portion of the work, so as to admit of the discussion of the 
auriferous quartz-lodes in their scientific and practical aspect, in 
the light of what has already been said on the general geology of 
the country. It is unnecessary to describe all the various forms 
and combinations in which lodes or veins of quartz occur • the 
principal have been already described in the numerous publications 
issued by the Mining Department, and it is enough to say that in 
every district, in every line of lode, and in every mine, differences 
may be observed, due, no doubt, to local conditions present at the 
time the voius were being formed, or to some subsequent move- 
ments and displacements of the rocks containing them. In fact; 
no two lodes are alike exactly, any more than two trees, though 
in general features a certain resemblance to a greater or less 
degree is traceable. 
A marked difference, however, may be observed in some respects 
between the reefs traversing Lower Silurian and those intersecting 
Upper Silurian rocks. In the case of the former, the voins 
traverse the rocks themselves, and, where dykes of igneous rock 
occur, these are usually found— as evidenced by the fact of their 
occasionally intersecting the quartz veins— to be of more recent 
date than the latter, and though frequently of value as guides to 
the miner, they do not appear to have in any way influenced the 
auriferous quality of the quarlz. 
In the Upper Siluriau rocks, the auriferous quartz-veins very 
frequently are found to traverse, accompany, or intersect from side 
to side, dykes of diorite of older date than themselves, and with 
the presence of which their auriferous quality appears to be closely 
associated. 
