81 
and in no case do they extend downward to any depth, but 
pinch out in less than a dozen feet; they are the fillings of 
wedge-shaped fissures within the diorite dykes. A typical 
instance of a 'reef" occurs one mile east of Krupp Hill. It 
measures four feet in width at the surface, but its walls 
rapidly converge to a point in depth. The fissure walls 
strike E. S'^ S., the northern wall dipping 60 S., the south- 
ern 80° S. The quartz is either milky or glassy. The for- 
mation may be termed a "dead lode,"* although pyrites is 
disseminated through the vein, and in one instance 
a trace of grey copper ore was discovered. 
The pyrites crystals that impregnate the mass 
are decomposed near the surface, leaving small cavities 
containing sulphur and a little limonite, the remaining pro- 
ducts of decomposition having stained the numerous cracks 
and crevices in the quartz. Slight quantities of secondary 
minerals (chlorite) occur locally, and the walls of small cavi- 
ties are coated with drusy quartz. 
Few miles west of Indulkana soakage a lode of siliceous 
ironstonef stands out conspicuously from a fissure in the 
crystalline schist. It is possible that this lode overlies a dio- 
rite dyke. 
Cambrian. 
No representatives of the Cambrian system were dis- 
covered in the vicinity of the north-western ranges, none of 
the contact rocks having disclosed any trace of organic re- 
mains in any shape or form. However, limestones that must 
without hesitation be correlated with the Cambrian strata of 
the Flinders Range occur at the head of Lake Torrens. The 
outcrop occupies but a small area at the surface, being about 
three miles in length, in direction east and west, by two 
miles north and south. The beds are massive, though they 
extend to no great vertical height above the general level of 
the country ; they stand as large, separated blocks resting 
upon a more compact body of rock below. The beds seem to 
strike westerly, although considerable variation (up to N. 
25° W., and more) were observed. On the southern limits 
of the exposure they have the form of a slight syncline, the 
dips of the strata on either side of the axis of 
folding being low (12° and 25° respectively). 
They are jointed vertically in two directions at 
right angles to one another. The rock mass, as a 
* One sample of this rock, that was subsequently assayed, re- 
turned a mere traoe of gold (accidental?). 
t Mr. H. Y. L. Brown has noted a "lode outcrop of ferrugi- 
nous quartzite and iron oxide" to occur in this locality, and is 
probably the same as that referred to. 
