Towards the end of Lower Carboniferous times, sedimentation, accompanied by widespread igneous activity, proceeded in a tectonically active, unstable and constricted basinal zone. Viséan flysch and olistostromic sequences were generated in front of an advancing deformation front which caused erosion of submarine rises and heralded the beginning of the Hercynian orogeny in this region.
Between Dartmoor and Bodmin Moor, Upper Devonian basin and rise facies sediments were thrust northwards over both Upper Devonian and Lower Carboniferous northern equivalents which were themselves incorporated onto the allochthon. The tectonic deformation history began in the late Viséan and early Namurian with the gravity sliding (Dl) of the bulk of the Lower Carboniferous northwards to form the Greystone Nappe. Subsequently the main thrusting event (D2) from late Lower Namurian times onwards led to the successive overthrusting and emplacement of the Heathfield, Petherwin and Tredorn Nappes. Towards the end of the Namurian and in the Westphalian the intrusion of the granite batholith caused the fold belt to tighten, which resulted in the formation of numerous low angle normal faults (D3) offsetting earlier thrusts to the N. Overall the regime is one of very thin-skinned thrust and nappe tectonics with the allochthon probably not exceeding 1 km in thickness.