The Sherwood Sandstone Group is a Triassic lithostratigraphic group (a sequence of rock strata) which is widespread in Britain, especially in the English Midlands.

Creswell Crags is an enclosed limestone gorge on the border between Derbyshire and Nottinghamshire, England. The cliffs in the ravine contain several caves that were occupied during the last ice age, between around 43,000 and 10,000 years ago.

The evidence of occupation found in the rich series of sediments that accumulated over many thousands of years is regarded as internationally unique in demonstrating how prehistoric people managed to live at the extreme northernmost limits of their territory during the Late Pleistocene period.

The name is derived from Sherwood Forest in Nottinghamshire which is underlain by rocks of this age.

Another property of the Sherwood Sandstones was that they could be dug into using hand tools. The sandstone were relatively weak and friable but thanks to a clay cement they could be shaped into self-supporting caves, with stable roof spans.

Contrary to popular legend and myth the caves did not form tunnels down which Robin Hood avoided capture by the Sheriff of Nottingham, but their history is no less interesting for that.

More Info: en.wikipedia.org