╭ Coal-Measures ╮ │ │ │ Millstone Grit │ CARBONIFEROUS ┤ │ │ Yoredale Rocks │ │ │ ╰ Mountain Limestone │ │ ╭ Devonian │ │ │ │ Upper Old Red │ DEVONIAN ┤ Sandstone │ │ │ │ Lower Old Red │ ╰ Sandstone │ │ ╭ Ludlow │ │ │ SILURIAN ┤ Wenlock ├ PALAEOZOIC │ │ ╰ May Hill │ │ ╭ Upper Bala │ │ │ │ Lower Bala │ ORDOVICIAN ┤ │ │ Llandeilo │ │ │ ╰ Arenig │ │ ╭ Tremadoc │ │ │ │ Lingula Flags │ CAMBRIAN ┤ │ │ Menevian │ │ │ ╰ Harlech ╯ LAVAS, ╮ VOLCANIC │ ASHES, │ GRANITOID ├ ARCHAEAN ROCKS AND │ SCHISTS OF │ ENORMOUS │ THICKNESS ╯ Fig 3.] I. =Archaean.= “Men can do nothing without the make-believe of a beginning.” GEORGE ELIOT.