On Cycadeoidea gigantea , a new Cycadean Stem from the Purbeck Beds of Portland

Abstract

The Isle of Portland has long been famous for the silicified Coniferous and Cycadean plants which occur in the surface-soils of Purbeck age. Buckland, Carruthers, and others have described the manner of occurrence and structure of the plant-remains from this horizon, and the fossil “crows' nests,” or short, thick stems of Cycads, have long been familiar to geologists. The plant which forms the subject of the following description was acquired by Dr. Woodward in 1895, and is now one of the most remarkable specimens in the Fossil Plant Gallery of the British Museum. It is probably the largest fossil Cycad hitherto recorded, and although the internal structure has been for the most part very imperfectly preserved, the cast of the stem is in some respects unusually complete. The specimen was found lying in a horizontal position in a bed of shaly clay, 2 feet thick, and about 17 feet higher in the Purbeck series than the Great Dirt-bed, from which most of the Portland plants have been obtained. The position of the fossil is shown in fig. 1; the section is drawn from a photograph of the rock-face in one of Mr. Barnes's quarries close to St. George's Church on the west side of the old Portland Wide Street. In Pl. I. the stem is represented about ⅛ natural size; it measures 1 metre 18·5 cm. At the base it is somewhat narrower and thinner, and the surface-features are less clearly shown than in the other