Further south there are newer Middle and Late Devonian rocks, known as Ilfracombe beds and Morte Slates. These include sandstone and limestone, which have been quarried near Aisholt. At Great Holwell, south of Aisholt, is the only limestone cave in the Devonian limestone of North Devon and West Somerset. The lower fringes around the hills are composed of younger New Red Sandstone rocks of the Triassic period. These rocks were laid down in a shallow sea and often contain irregular masses or veins of gypsum, which was mined on the foreshore at Watchet.