III.—The New Red (Permian) Gravels of the Tiverton District

Extract

The New Red gravels of the Tiverton type extend from Warbrightsleigh and Chimney Down on the north to Thorverton and White Down Copse on the south. Further south they are replaced by breccias and sandstones or covered by the higher beds of the New Red series. Throughout the whole of this area of nearly 100 square miles the gravels contain fragments of sandstone and grit with Upper Devonian fossils. These Devonian fragments are most common in the north-east of the district, and are comparatively rare further south. They are found at the entrance of the Crediton valley, but do not appear to be present further west.

All the fossils that have been identified are known to occur in the Pilton and Marwood Beds of North Devon. The only Trilobite found (Phacops latifrons, Bronn) is practically the only Trilobite occurring in the Pilton Beds, where it is very common. Spirifer Verneuili, Murch., Spirifer Urii, Flem., Rhynchonella (Camarotæchia) Partridgiæ, Whidb., and Productus prælongus, Sowerby, are the commonest Brachiopods both in the gravels and in the Pilton Beds. The little Gasteropod Euomphalus vermis, Whidb., is also common in the gravels and Pilton Beds. Bellerophon subglobatus, M'Coy, is a characteristic fossil in the Marwood Beds of the Barnstaple district; it is also common in the grits that occur further east near Wiveliscombe, and in the grit fragments found in the gravels.

At Chimney Down, in the north-east of the district, fossiliferous fragments of Upper Devonian sandstone and grit are extremely common, whilst trap fragments appear to be absent. This fact, as well as the wide distribution of the fossiliferous fragments, completely disposes of the Rev. W. Downes' theory of volcanic ejection. The facts tend, rather, to prove a drift from the north-east during the period of deposition of the gravels. The grit and sandstone matrices suggest a derivation from the Wiveliscombe end of the Pilton Beds rather than from the more slaty beds found further west. The Devonian fragments in the gravels may even have been derived from a still more easterly extension of the Pilton Beds, now buried under Triassic deposits.