Note 94 — Chapter X · THE CAMBRIAN VOLCANOES OF SOUTH WALES
Reading edition
Dr. Hicks has noted the occurrence of "volcanic tuff" in the Lower Lingula Flags of Porth-y-Rhaw, a little to the east of St. David's (Quart. Journ. Geol. Soc. vol. xx. 1864, p. 240). This intercalation is marked as a "dyke" in the MS. notes of Sir A. C. Ramsay on a copy of the Geological Survey map of the district.