At Akaroa and the outer bays, you are looking at an ancient part of New Zealand.
There is a small area of rocks that are thought to date back 240 million years. And near those ancient rocks is an area of rocks that are younger, but still date back to a period enormously distant from today — 90 million years.
About 65 million years ago Banks Peninsula was sea bed; a large area of land submerged beneath the Pacific Ocean. The sand and mud that was washed onto that sea floor became compacted and under enormous pressures changed into sedimentary rock. And the fine sandstone at Charteris Bay has been quarried and used as a popular, effective building stone in many Canterbury buildings.
At Charteris Bay you can see thin layers of rocks formed from marine sands about 20 million years old. This tells us the peninsular was still under water that time.
But by about 15 million years ago the peninsular had obviously been lifted up off the sea floor and pushed above the water to form dry land. Quite likely this was 'triggered' by the initial stirrings of a great upheaval known as the Kaikoura Orogeny. This was a complicated earth movement that formed the Southern Alps and fashioned much of New Zealand as we know it geologically. But geologists think the Kaikoura Orogeny didn't actually affect the structure and shape of what became bank Peninsular. The underlying rocks remained in place and the shape of the ancient major valleys was determined by the volcanoes that began to erupt across the peninsular at the time we are talking about htere — some 15 millions years ago.
These first volcanoes erupted at Governor's Bay, in the Lyttleton Harbour. And you can still see rocks left behind from that time.