23 i 



The Portland Oolite is well exposed at Swindon, Tisburj, 

 Chicksgi'ove, and other places in the vale of Wardour, Wilts ; 

 at Shotover, Oxon ; at Hartwell, near Aylesbury ; at Brill and 

 Stone, Bucks ; and in the island of Portland and other localities 

 in Dorset. It consists of Sands and Sandstones below, gradually 

 becoming calcareous as we ascend, and passing into light- 

 coloured Limestones above. Many of the beds contain layers 

 of chert, alternating with them like flints in the upper cretaceous 

 rocks. The Portland beds are divisible into — 



a. Portland stone, consisting of fine white calcareo-siliceous 

 Limestones with oolitic structure, and known locally as 

 "Stonebrash" and "Eoche" by the workmen; with these 

 are interstratified layers of clay and masses of chert, 90 feet 

 thick. 

 h. Portland sands, consisting of brown and yellow sands, and 

 sandstone, the lower portion full of green grains of the 

 silicate of iron, Glauconite, 80 feet, 

 c. Kimmeridge clay. 

 Several very fine sections are exposed in different quarries 

 in the island of Portland, where the marine beds of the 

 Portland Oolite are overlain by the estuarine series of Purbeck 

 beds, consisting of clays and limestones crowded with freshwater 

 mollusca, the soil of old land or "dirt beds," with the roots 

 and stems of trees, Cycadece seen in the position in which they 

 grew prior to their submergence beneath the Neocomian wave. 

 A very interesting section of upper oolitic strata is seen in a 

 hill near Hartwell, by Aylesbury, where the Portland, Purbeck, 

 Wealden, and Neocomian strata are found in position resting 

 on Kimmeridge clay, which is worked for brickmaking, and 

 contains many fossils in fine preservation, as Ammonites hiplex, 

 Belemnites Souichii, Astarte Hartwelliensis, with the bones of 

 Pliosaurus. My late friend, M. S^mann of Paris, examined 

 this locality and made a section of the beds in 1866, with the 

 intention of correlating the English Portland beds with the 

 Portlandien stage, which he had previously studied at Boulogne- 

 sur-Mer. His notes and section have been published by my 

 friend M. P. de Lokiol and M. E. Pellat in their Monograph 

 on I'etage Portlandien des environs de Boulogne-sur-Mer. 



