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Letters printed on a map naming the rock's age.
Also known as: Stratigraphic letter codes, Map period codes
Letter codes printed within coloured areas name the geological period — C for Carboniferous, K for Cretaceous, J for Jurassic. K rather than C for Cretaceous comes from the German Kreide, which is why the letters are not simply initials of the English names.
Name the geological period of a mapped rock unit with one or two letters printed within its coloured area.
Contexts: Technical drawing, Maps
Do not follow English initials throughout: K for Cretaceous comes from the German Kreide, chosen because C was already taken by Carboniferous.
Contexts: Technical drawing, Maps
One or two capital letters, sometimes with a small suffix, printed within a coloured area on a map.