The rock strata known as the Carboniferous Limestone were laid down during the early Carboniferous Period, about 320–350 million years ago.[5] Subsequently, much of northwestern Europe underwent continental collision throughout the late Paleozoic Era, culminating in the final phases of the Variscan orogeny near the end of the Carboniferous, 300 million years ago. This tectonic activity produced a complex suite of mountain and hill ranges across what is now southern Ireland, south-western England, Brittany, and elsewhere in western Europe.[6]