The greenish grey rocks on the right of the picture are an Ignimbrite, part of the Llandovery Skomer Volcanic Group, Marloes Sands, Pembrokeshire, Wales.The interface between basalt (left) and Ignimbrite (right) is visible. Ignimbrites are deposited from pyroclastic flows following a violent volcanic explosion, these igneous rocks are interbedded with Silurian sedimentary rocks from the Jukes Brown coralliferous group which is approximately 428 million years old.