 For a relatively short time of 5 million years Ordovician volcanoes ejected the Borrowdale volcanic rocks – firstly lavas (mostly andesite} and later pyroclastic rocks found in the more central part of the region.The ejection of rock was extreme by world standards and it produced deposits at least deep.When the Baltica-Avalonia and Laurentia continents collided some 420 million years ago in the Caledonian orogeny there was folding of the slate and fracturing (faulting) of the more brittle volcanic rock.