Bellevue ASSI

Bellevue is a special place because of its earth science interest. The area provides access to an infrequently exposed deposit called the Clay-with-flints (CwF). This deposit is found between the Cretaceous white limestone below and the Palaeogene black basalt above and spans a period of time of approximately 10 million years. Because of its location beneath the basalt, the CwF is usually only exposed at the edge of the Antrim Plateau.

The Cretaceous white limestone formed on the bottom of a sea floor around 75 million years ago, during a time when the island of Ireland was completely covered by a warm, clear, shallow sea. As the sea level eventually dropped, the resulting limestone was exposed and it underwent a long period of weathering. This would have led to the development of a landscape similar to that of the Burren in Co. Clare, with abundant limestone pavement and associated hollows and caves. The Cretaceous limestone contains abundant nodules and layers of flint, a silica-rich material that does not dissolve in rainwater, unlike the limestone. As weathering continued, it left behind the more robust flints that accumulated on the limestone landscape.

Bellevue consists of a line of disused quarries exposing both the white limestone below and the black basalt above. The CwF is exposed both at the northern end and at the southern end of the site.

The most striking elements of the exposures at Bellevue is the uneven surface at the top of the white limestone that is clearly visible in the cliff face. This is a result of the weathering that took place after the fall in sea level at the end of the Cretaceous period. Due to this uneven surface, the thickness of the CwF varies greatly from only a few centimetres to over 2 metres.