< erberg| | a | \Gedinnian. | _Cephalaspis_, | | \ Group.| | r | | _Pteraspis_, &c. | \ Oriskany Sandstone. | | y +---+------------------+------------------------+----------------------------------+ | . | | | / Lower Helderberg Group. | | | S | / Ludlow Group. | | Water-Lime. | | | i | Upper < Wenlock " | < Niagara Shale and Limestone. | | | l | \ Llandovery" | | Clinton Group. | | | u | | \ Medina " | | | r | | | | | i | | / Cincinnati Group. | | | a | Lower / Caradoc or Bala Group. | | Utica " | | | n | (Ordovician) < Llandeilo " | < Trenton " | | | . | \ Arenig " | | Chazy " | | | | | \ Calciferous " | | +---+-------------------------------------------+----------------------------------+ | | C | Upper or _Olenus_ series--Tremadoc | Upper or Potsdam series with | | | a | slates and _Lingula_ Flags. | _Olenus_ and _Dicelocephalus_ | | | m | Middle or _Pardoxides_ series--Menevian | fauna. | | | b | Group. | Middle or Acadian series with | | | r | Lower or _Olenellus_ series--Llanberis | _Paradoxides_ fauna. | | | i | and Harlech Group, and _Olenellus_- | Lower or Georgian series with | | | a | zone. | _Olenellus_ fauna. | | | n | | | | | . | | | +---+---+-------------------------------------------+----------------------------------+ | | | Archean, Pre-Cambrian, Eozoic. | +---+---+-------------------------------------------+----------------------------------+ | | | In Scotland, underneath the Cambrian | In Canada and the Lake Superior | | | | Olenellus group, lies unconformably | region of the United States | | | | a mass of red sandstone and con- | a vast succession of rocks of | | | | glomerate (Torridonian) 8000 or 10,000 | Pre-Cambrian age has been | | | | ft. thick, which rests with a strong | grouped into the following | | | | gneisses and schists (Lewisian).