Ireland was once two islands with the Mountains of Mourne as hot as California's Death Valley, a new book revealed today.
Lava formations from primeval days helped provide the foundations for Carrickfergus Castle`s defences, the work by Belfast author Paul Lyle said.
Between Rocks And Hard Places links scientific, mythological and archaeological data. Published by the Geological Survey of Northern Ireland the book tells how Earth shaped Ireland's dramatic landscapes.
Mr Lyle said: "This area is exceptional for its natural beauty and rich heritage, but more than most ever realise. To the envy of many around the globe, it is possible for anyone here to easily see and examine rocks across almost the entire range of geological time.
"This book aims to reveal how we can read the rocks and decode the secrets of our distant past and the tremendous events that have moulded the natural and cultural landscapes we now know."
It describes how two islands an ocean apart joined to form Ireland. The publication shows how the deserts of Co Down were as hot as Death Valley.
Garth Earls, director of the Geological Survey, contributed to the book.
"For its size, the northern third of Ireland hosts as great a range of rock types and rock ages as you can find in Europe or indeed further afield.
"It has been incredibly influential, inspiring rich folklore, contributing to key historical events and continues to shape the very way we live our lives today."