The Ilfracombe Slates are overlain in turn by the Morte Slates Formation of Frasnian to Famennian age. Extending east from Challacombe, the slates provide much of the high ground south of the B3358 road through Simonsbath and Exford including Setta Barrow and form the Brendon Hills before extending to the easternmost extremity of the park at Elworthy.