SOME GEOLOGICAL NOTES ON COUNTRY BEHIND JERVIS BAY. 307 
cherts ; the folded and contorted strata to the west consist 
of similar cherts and quartzites above and limestone below. 
The limestone was determined by an exposure in the main 
branch of the Httrema to have a thickness of about 500 
feet or more. 
The main fissure (thrust plane?) cuts the creek in several 
places and seems to contain the best ore and the ore body 
has a maximum width where exposed of from 6—8 feet. It 
consists of argentiferous galena, zinc-blende, chalcopyrite 
and mispickel. The secondary fissure which cuts the anti- 
cline runs almost due north and south, dips (underlies) to 
the east at an almost vertical angle, and the lode is of great 
size, having a width in the bed of the creek of over 20 feet. 
The eastern half of the lode contains galena, but the 
western half is almost pure zinc blende. Both these fissure 
lodes appear to thin out and bifurcate upwards and to 
thicken downwards. From their direction and dip it is 
clear that they will meet at a depth. 
In addition to these two fissure lodes there are numerous 
bedded veins varying from 6 inches to 3 feet in thickness, 
forming huge floors of ore. These occur in great abundance 
in the folded strata west of the creek and may extend for 
hundreds of yards into the adjacent mountain. The bedded 
veins contain a more complex grade of ore than the fissure 
lodes, being very rich in arsenical pyrites. They constitute 
replacement deposits in limestone. 
All the rocks on both sides of the creek are of Devonian 
age and pitch to the north. They were probably folded in 
the Carboniferous period. The intensity of the folding 
movements led to fracturing, and metallic solutions rose 
along the fissures and precipitated their contents on the 
walls. On reaching the limestone they filtered along the 
bedding planes and dissolved out carbonate of lime leaving 
metallic sulphides instead. The source of the minerals 
