The Mesozoic and Tertiary strata of Hawke's Bay include many sequences of vertically graded, banded sediments, some of which are contemporaneous with sequences of massive sediments deposited in nearby localities. The distribution of the thickness of sediments in Central Hawke's Bay, indicates that a trough-like basin existed in the upper Miocene. Into this basin a thick sequence of banded' sediments was deposited, while at the same time a thin sequence of unstratified beds was laid down in the area surrounding the basin. An investigat10n of the grain sizes in the basin revealed a decrease in grain size in a westerly direction. The sediments were brought in from the east, presumably across a bar which is thought to have separated the basin from the open ocean.