Looking at the landscape around Sydney now, it’s hard to believe that at one stage the area harboured some active volcanoes. The evidence may be hard to find now, but they are there.

Back to the geology excursion, the second half was a visit to Kulnura Quarry, in the tablelands of the Central Coast. The quarry produces basalt to be used in concrete and road base, and basalt (recalling all those high school science lessons) comes from volcanoes.

We could drive into the quarry. Here we are at the top of the hill.

We drive 160 metres down to the floor of the quarry.

And look back up to where we started.

That’s 50 years worth of digging – and they still haven’t hit the bottom. The manager said that there’s another 50 years’ worth of basalt underneath.