To log this cache, you must provide me the four words I require
from the sign at the listed co-ordinates - and an age you must
determine from the diagram once you have identified the rock type I
am interested in. You can record your log at the same time as
messaging me - I will delete your log and let you know if you
haven't answered my questions properly.
The eruption of lava created a plug that was
(1)______________(1) shaped.
The lava (2)____________(2) (3)____________(3) and
(4)____________(4), creating the slabby rock.
Now that you have identified the slabby rock, I want you to tell
me how many million years old it is (to the nearest 1 million
years).
To log your find, you need to send the four words
(1)-(4), and the age of the rock.
From the Halswell Quarry Park Management Plan 1998.
The Port Hills originally formed part of the western
side of a shield volcano. which reached a maximum height of
approximately 1500 metres about 10 million years ago. It was active
for approximately two million years, during which time the lavas
built up a symmetrical cone. Rock formations on the Port Hills
adjacent to the Halswell area are largely basalts of the Lyttelton
Group. The Halswell Quarry site is an isolated area of dark grey
lavas which were extruded about 6 million years ago. The basalts of
the ridge and spurs are of a high quality, being particularly
hard.
The nature of the jointing has made some of the rock valuable as a
decorative facing stone. However, most of it was crushed for use as
road metal. There is also a high content of volcanic ash (scoria).
While the quarry officially closed at the end of 1990, a small
remaining area of dimension stone has been located and can be
extracted when required.
The quarry’s geological exposures show a wide variety of volcanic
material, offering an excellent opportunity for illustrating
volcanism.
Much of the area has been overlain with loess - most of it
probably deposited during glacial periods, but with considerable
re-deposition from higher slopes. As far as can be determined, the
spur immediately east of the existing quarry is composed
predominantly of scoria and loess and only occasional outcrops of
rock. It does not contain any economically significant quantities
of rock. The level ground, adjacent to Kennedy’s Bush Road and
Cashmere Road, is, like most of the Canterbury Plains, underlain by
uncemented river gravels.