Complex sentence: The youngest rocks intruded by the granites, the Carboniferous Crackington and Bealsmill formations of Namurian to lower Westphalian in age, provide a lower bound for the timing of granite emplacement of about 310 Ma.
Split into simpler sentences: The youngest rocks into which the granites intrude are the Carboniferous Crackington and Bealsmill formations of Namurian to lower Westphalian age. This provides a lower bound for the timing of granite emplacement of about 310 Ma.