Holkerian

The Holkerian is a sub-stage of the Viséan stage of the International Commission on Stratigraphy (ICS) geological timescale. It is one of five sub-stages commonly used in the Viséan stage within stratigraphy by British, Irish and other geologists outside the US and Asia.

As part of the Viséan, Holkerian rocks were formed about 339 to 335 million years ago, in the Early Carboniferous subperiod. Rock formations laid down in this time were frequently different types of fossiliferous limestone. The material for all these rocks was laid down in warm, sub-tropical marine conditions of the time when north-western Europe was close to the equator.