Formation. Prevailing Rocks. Thickness. Fossils.
Lower { Hard sandstones, conglomerates, { 600 to } Pentamerus lens.
Llandovery { and flaggy shaly beds { 1,000 }
{ Shelly sandstones, shales, and } { Brachiopods;
{ slaty beds, with grits, con- } { Lamellibranchs;
Caradoc or { glomerates, and occasional } 12,000 { Pteropods;
Bala { calcareous bands (Bala lime- } { Cystideans;
{ stone) } { Graptolites;
{ } { Trilobites.
{ Dark-grey flagstones, occasionally }
Llandeilo { calcareous sandstones, }
Flags { with black slates, containing } { Trilobites
{ Graptolites } 1,000 { (Fig. 36);
{ } to { Graptolites;
} 1,500 { Heteropods;
Lower { Dark-grey and ferruginous } { large
Llandeilo { slates, sandy shales, and bluish } { Cephalopods.
Tremadoc { flags, with occasional beds }
Slates { of pisolitic iron-ore }
{ Trilobites
{ Black and dark shaly, grey } { (Olenus,
{ and brown slaty flagstones } { Conocoryphe,
Lingula { and sandstones, with siliceous } 6,000 { Paradoxides,
Flags { grits and quartzites } { Fig. 17);
{ } { Brachiopods;
{ } { Cystideans.