The Antrim Lava Group (Palaeogene) is subdivided into the Lower Basalt Formation, the Interbasaltic Formation and the Upper Basalt Formation. The base of the Lower Basalt Formation is formed, in many places, by a 1.0-1.5m thick unit of structureless brick-red, blue or grey clay with scattered and locally reddened flints. The ‘clay-with-flint' horizon, which often forms an infilling to surface hollows in the underlying Ulster White Limestone Formation had previously been interpreted as representing a ‘terra rozza' type soil deposit that developed by deep weathering of the top of the Ulster White Limestone prior to the eruption of flood basalts. The old quarries at Bellevue are one of the best localities to see this horizon in the Greater Belfast area.
The section comprises of:
TOP LAYER: 30-40cm
Deep brown-red flint-rich clay matrix, clast-supported clay.
BASAL LAYER: 60-70cm
Salmon-brown clay-supported layer with discrete small-to-large grey flints up to 25cm across concentrated near the base.