Graham Eaton / The Norber Erratics. Blocks of older Silurian sandstone, perched on top of younger Carboniferous limestone, that were left by retreating ice at the end of the last Ice Age, Clapham, Yorkshire, winter

Graham Eaton / Limestone pavement above Malham Cove, Yorkshire

SINCLAIR STAMMERS / Well preserved fossil of trilobite Dudley locust (Calymene blumenbachii) from the Silurian period, found in the Wenlock Limestone of Wrens Nest Hill, Dudley, Worcestershire.

Paul D Stewart / A rare British broadsheet illustration with contemporary hand colouring, drawn and engraved by John Emslie and published by James Reynolds in 1849. It shows reconstructions of extinct creatures in the...

Graham Eaton / A glacial erratic of Silurian age sandstone, perched upon younger Carboniferous age limestones. The limestone forms a limestone pavement with the hill , Whernside, Yorkshire, England, UK.

Graham Eaton / Glacial erratic of Silurian age sandstone, perched upon youger Carboniferous age limestones. The limestones form a limestone pavement with the hill Ingleborough in the background. Whernside, Yorkshire...

Graham Eaton / An erratic of Silurian sandstone sitting on Carboniferous limestone at Twistleton Scar above Ingleton, with Ingleborough in the backgrond, October. Whernside, Yorkshire, England, UK.

Graham Eaton / A Glacial Erratic at Norber near Austwick, Yorkshire, UK. This is one of the Norber erratics, where blocks of older Silurian sandstone were left on top of younger Carboniferous limestone by a retreati...

Graham Eaton / A Glacial Erratic at Norber near Austwick, Yorkshire, UK. This is one of the Norber erratics, where blocks of older Silurian sandstone were left on top of younger Carboniferous limestone by a retreati...

Graham Eaton / A Glacial Erratic at Norber near Austwick, Yorkshire, UK. This is one of the Norber erratics, where blocks of older Silurian sandstone were left on top of younger Carboniferous limestone by a retreati...

Graham Eaton / Steeply dipping beds of Silurian age turbidite sediments, Clarach Bay, Aberystwyth, Wales, UK, September 2014.

Graham Eaton / Pistyll Rhaeadr, a waterfall located a few miles from the village of Llanrhaeadr-ym-Mochnant in Powys, Wales, UK. The river / Afon Disgynfa falls 73m down a cliff face of Silurian rocks - one of the s...