carboniferous
Carboniferous (adj) means relating to a period of geological time within the Palaeozoic era, made up of the Mississippian and Pennsylvanian epochs (each divided into lower, middle and upper stages), lasting between about 345 and 280 million years ago, the era in which coal was formed.
Etymology
This comes from carboniferous ("producing carbon"), which was formed from carbon, -i-, and -ferous.