A large slab of dolerite is exposed on the seashore of Cartwright Reserve. It was formed during extensive volcanic intrusion of [country] rock 200-160 Mya (Jurassic Period), when the supercontinent of Gondwana began to break up. Dolerite is common in the Hobart area and forms the hills of kunanyi, Knocklofty and Taroona.
Good examples of the characteristic spheroidal weathering in dolerite boulders can be seen here. The foreshore is also a good site to consider the fault-and-graben system of the hills and valleys around the Derwent: formed by a complex system of deep faulting during the breakup of Gondwana.
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