Published online by Cambridge University Press: 01 May 2009
Quarrying activity adjacent to the well-known intrusion of monchiquite cutting Old Red Sandstone near Usk, in Monmouthshire (originally described by W. S. Boulton, in 1911), shows that the monchiquite proper is associated with an agglomerate-filled vent. Fossiliferous blocks contained within the agglomerate (first recorded by C. R. K. Blundell) show that the volcanic activity took place not earlier than in Lower Carboniferous time; and throw light on the former extension of the Carboniferous Limestone in this area.