{ {Magnesian Limestone and Sandstone } Red Sandstones {Permian {Marl Slate } and Magnesian { {Lower Permian Sandstone } Limestone P{ R{ {Coal Measures } Sandstones, Shales I{Carboniferous {Millstone Grit } and Coals at top M{ {Mountain Limestone } Sandstones in A{ {Basal Carboniferous Rocks } middle Limestone R{ } and Shales below Y{ { {Upper } Devonian and old Red } Red Sandstones, {Devonian {Mid } Sandstone } Shales, Slates and { {Lower } } Limestones { { {Ludlow Beds } Sandstones, Shales {Silurian {Wenlock Beds } and Thin { {Llandovery Beds } Limestones { { {Caradoc Beds } Shales, Slates, {Ordovician {Llandeilo Beds }Sandstones and { {Arenig Beds } Thin Limestones { { {Tremadoc Slates } {Cambrian {Lingula Flags } Slates and { {Menevian Beds } Sandstones { {Harlech Grits and Llanberis Slates } { { {Sandstones, {Pre-Cambrian No definite classification yet made {Slates and {Volcanic Rocks [Illustration: DIAGRAM SECTION FROM SNOWDON TO HARWICH, ABOUT 200 MILES. This cross section shows what would be seen in a deep cutting nearly E. and W. across England and Wales. It shows also how, in consequence of the folding of the strata and the cutting off of the uplifted parts, old rocks which should be tens of thousands of feet down are found in borings in East Anglia only 1000 feet or so below the surface.]