Auriferous Quartz-veins. 
119 
It is scarcely to bo imagined that all the fissures now occupied 
by quartz-veins were formed within one short period. No doubt 
most of them resulted from movements connected with or closely 
following the corrugation of the strata, whether that process was 
accomplished quickly or slowly; but with succeeding movements 
further fissures and displacements were effected from time to time, 
thus rendering the systems of fissures or lines of fracture more and 
more complex. The existence in Upper Palieozoic rocks of quartz- 
veins traversing conglomerates, which are themselves partly com- 
posed of rounded pebbles of vein-quartz, is in itself a clear proof 
that the formation of quartz-veins in fissures was not confined to 
the Silurian rocks, though it attained its extreme development in 
them. At the same time, it would appear that most of the 
fissures occupied by quartz-veins in Silurian rocks in Victoria 
were formed and occupied by their contents prior to the formation 
of the Upper Palaeozoic rocks. 
With regard to the direction and extent, of the fissures, much 
depended on the character of the rocks they occurred in. In 
evenly-bedded slates the fissures would generally be regular, while 
in diorite dykes the shrinkage cracks would naturally be irregular, 
though the fissures, if any, along the walls of the dykes would bo 
influenced, as regards regularity or otherwise, by the character of 
tho containing rocks. In one case a clean fissure or split between 
two parallel rock-bands would be effected. In a second, the fissure, 
owing to some conditions in the directions of the operating forces, 
or the tenacity of the rock-bands, would follow the planes of 
stratification, either horizontally, but not vertically, or would 
intersect them obliquely in both directions. In a third instance, 
an abnormal displacement would cause a fissure of which one 
wall was clean — i.e., the piano surface of a rock -layer — and tho 
other wall irregular, on account of tho plane of the former cross- 
ing obliquely the basset edges of the layers in the latter. 
Numerous other cases and combinations might he instauced, but 
the- above are the principal, ami serve to illustrate the phenomena 
now observable in mineral lodes and veins. Fissures also occurred 
along different portions of which all the conditions mentioned were 
developed. Tho course of a fissure diverged from botween two 
parallel bands, and passing downwards, or laterally through one 
wall, established the conditions described in the second case, 
whence it passed into tho third, &c. 
Whore plutonic or hydrothormal action resulted in the injection 
of dykes, wo find that while some of those dykes found their way 
along tho lines of least resistance or with the strike of the rock- 
bands, others intersected the latter across their line of strike, either 
obliquely or at right angles. 
Admitting generally that the fissures resulted from movements 
of the earth’s crust and the fracturing thereby of the rock-masses, 
