The Ordovician had Shropshire back to volcanic activity, and saw the county temporarily split in two, along the Pontesford – Linley fault line. Everything west of this line was ocean, while the east was dry land. The Iapetus Ocean was closing, bringing the two halves of Britain towards each other, and volcanic eruptions created the Cumbrian Mountains and Snowdonia. Shropshire also saw volcanic activity. To the west of the Pontesford – Linley fault, volcanic rocks have been found. The other side of the fault line was quieter. The land was slowly eroded, and the sea gradually flooded it, so that only the tops of hills could be seen, such as the ancient Caer Caradoc. Towards the end of the Ordovician, the sea levels dropped, due to another ice age. An interesting observation of this erosion can be found in the stratigraphy as a sea stump (an eroded sea stack).