THE OLIGOCENE 67 



the surface. The Lower Marls consist chiefly of variously- 

 coloured clays with many shells, chiefly Cyrena pukhra, 

 semistriata, and obovata, Cerithium mutabile, and Melania 

 muricata (acuta) ; and red and green marls, in which are 

 few shells, but fragments of turtle occur. A little above 

 the oyster bed is a band of hard-bluish septarian limestone. 

 Sixty years ago Edward Forbes remarked on the re- 

 semblance of this band to the harder insect-bearing 

 limestones of the Purbeck beds. In a limestone exactly 

 resembling this, and similarly situated in the lower part 

 of the marls in Gurnard and Thorness Bays, numerous 

 insects were afterwards found, beetles, flies, locusts, and 

 dragonflies, and spiders. Leaves of plants, including 

 palms, fig, and cinnamon, have also been found in this 

 bed, showing that the climate was still sub-tropical. 

 The upper Marls consist chiefly of grey clays with abund- 

 ance of Melania turritissima (Potamaclis) . The chief 

 shells in the marls are Cyrena, Melania, Mclanopsis 

 and Pahidina (Viviparns). They are often beautifully 

 preserved ; the species of Cyrena often retain their colour- 

 markings. 



Bembridge Foreland is formed by a thick bed of flint 

 gravel resting on the marls, which are seen again in Priory 

 Bay, where in winter they flow over the sea-wall in a semi- 

 liquid condition. They lie above the limestone at Gur- 

 nard, Thorness, and Hamstead. West of Hamstead Ledge 

 the whole of the beds crop out on the shore, where beauti- 

 fully preserved fossils may be collected. Large pieces of 

 drift wood occur, also seeds and fruit. Many fragments 

 of turtle plates may be found. Large crystals of selenite 

 (sulphate of lime) occur in the Marls. 



Last of the Oligocene in the Isle of Wight are the 

 Hamstead beds. These strata are peculiar to the Isle of 

 Wight. The Bembridge beds also are not found on the 

 mainland, except a small outlier at Creechbarrow Hill 

 in Dorset. The Hamstead beds consist of some 250 feet 



