Rowley Hills quarries and dolerite
These basalts and dolerites were intruded in a hot ( >1000°C) molten state into strata of the Coal Measures and Etruria Marls late in the Carboniferous period (in Westphalian D times) as a result of major earth movements of the Hercynian mountain building episode that were occurring at this time. The magmas slowly cooled at depth and formed the hard crystalline rock that is locally called today the ‘Rowley Rag’.
