Stirling Point, Bluff

The background Permian gabbro is a coarse grained plutonic rock with interlocking 1-5mm crystals of white plagioclase feldspar and black pyroxene. This is the oldest rock. The next oldest rock is a pale orange granite and the youngest intrusive rocks are the straight sided, fine grained black basalt dikes.

At first sight the rock platforms look like a mess of cracks, fractures and dark coloured rock. But take your time, walk around and get your eye in. The straight, black basalt dikes are the easiest to spot. About 50 m SSW from the lighthouse a pair of pale orange coloured, irregular-sided pod-like granite dikes strike (trend) SW for a short distance. They are cut by basalt dikes that trend SE. The background (most abundant) rock is the medium grey gabbro. The cross-cutting relationships of the gabbro, granite and basalt are important because they give a relative age sequence of the rocks. Have a look to find the evidence that shows which are the oldest, the next oldest and the youngest rocks.