In 1908 Dr. Rowe published an account of the Chalk of the Isle of Wight with a zonal map in which the zone of Belemnitella mucronata was shown as entirely absent at some points but generally present in substantial thickness. At the two ends of the island actual measurements were made, of 150 feet at Culver Down and 475 feet at the Needles. How much of the latter thickness was measured in the cliffs and how much is made up of somewhat less satisfactory measurements at low tide on weed-covered reefs is not clear, but at any rate there must be well over 300 feet in the cliffs. This figure is sufficient to show how great a ravining of the pre-Tertiary surface of the chalk would be required for the repeated disappearances of the zone as mapped. It seems justifiable to pay some critical attention to the evidence on which such a state of things is alleged.