The latest Cretaceous is the Ripley formation, which lies west of the northern part of the last-named, and, about Scooba, in a small strip, the most southerly of the Cretaceous - it is composed of coarse sandstones, hard crystalline white limestones, clays, sands, phosphatic greensands, and darkcoloured, micaceous, glauconitic marls; its greatest thickness is about 280 ft.
Geologically the region is made up of Carboniferous limestones, clay slates and sandstones, containing anthracite and coal; of Cretaceous marls, chalk, sandstone and greensands - chalk cliffs, in fact, accompany the Don for 200 m.; and of Miocene limestones and clays.
These Cretaceous limestones are interbedded with glauconitic greensands, as at Moeraki Point in eastern Otago.
The next deposits, as the scarps are approached, are greensands of "Selbornian" age, succeeded by Cenomanian, and locally by Turonian, sands.
The narrow strip of Greensands appearing from beneath the Chalk escarpment on its northern side is crowded with small towns and villages on account of the plentiful water-supply.