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.
In some species the adults assume a darkcoloured head every breeding-season, in others any trace of dark colour is the mark of immaturity.
At the end of a fortnight the white spat has become darkcoloured from the appearance of coloured patches in the developing embryos.
The hills consist of a kind of granite and of beds of red sandstone, the disintegration of which has given a darkcoloured ferruginous soil of moderate fertility.
The developing seed thus encloses fungal hyphae, which remain dormant within the seed and in spring develop symbiotically with the growth of the wheat plant, doing no apparent injury until the time of fruiting is reached, when the fungus takes complete possession and fills the new seed with a mass of darkcoloured spores.