Schist rock outcrops in Flat Top Conservation Area near Alexanda, New Zealand. The Dam and its outlet tunnel (728 metres through solid schist rock) were built between 1935 and 1937 to create a water reservoir for nearby Alexandra but today is used for irrigation. A dry land ecosystem, Flat Top Hill supports a diverse range of animal and plant life, including examples of regenerating native plant species that previously covered much of the lowland valleys of Central Otago. This is one of New Zealand's most threatened habitats.