476 STRATIGRAPHICAL GEOLOGY 



that the remains of Iguanodon and Hyheosaurus were first dis- 

 covered by Dr. Mantell, and the specimens which he figured and 

 described are now in the South Kensington Museum. 



The uppermost member of the Wealden Group consists mainly 

 of brown and blue clays, with layers of shelly limestone and occa- 

 sional beds of sand and calcareous sandstone. The limestones are 

 known as Sussex marbles, and are composed almost entirely of 

 Viviparus shells, those in the lower part of the clay consisting 

 chiefly of V. sussexensis, while the most constant band (the Pet- 

 worth and Bithersden marbles) consists of V. flumorum. The 

 minute freshwater Crustaceans (Gypridea) are also very abundant 

 in some places, the surfaces of the more shaly beds being crowded 

 with them. Unio and Cyrena also occur. At Haslemere the 

 highest beds, just below the Atherfield Clay, contain Corbula and 

 Mytilus, as well as Cyrena and Melanopsis, indicating the change 

 from freshwater to marine conditions. 



In the Isle of Wight Wealden Beds are exposed both on the 

 eastern and western sides (see map, Fig. 172). The equivalent of 

 the Hastings sands is not visible ; the lowest beds seen are 

 those at Brook Point in Compton Bay, and consist of a pale sand- 

 stone overlain by red and green marls in which the broken trunks 

 of pine trees are so numerous that it would seem as if a raft of 

 waterlogged trees had here sunk to the bottom, a frequent occur- 

 rence in the deltas of large rivers like the Mississippi ; the spot is 

 known to local geologists as the "pine -raft." The higher beds, 

 consisting of variegated marls or clays with thin beds of sand- 

 stone, can be seen by walking along the coast to the southward ; 

 they have yielded bones and footprints of Iguanodon, Hypsilophodon, 

 and other reptiles, with Unio valdensis, but other fossils are rare 

 in this lower division, which has a thickness of about 700 feet. 



The higher beds are well exposed between Cowleaze Chine and 

 Atherfield Point ; they consist almost entirely of grey shales with 

 some beds of sandstone, ironstone, and limestone. These beds are 

 much more fossiliferous, containing species of Meta, Cypris, Gypridea, 

 and Gandona, with Cyrena, Viviparus, and Vicarya (a sub-genus of 

 Potamides). Small oysters also occur near the top. This series of 

 beds is about 200 feet thick, and is directly overlain by the 

 " Perna Bed " J^ en t, ioned below. 



The whol o f the Wealden comes to the surface near Swanage 

 iri Dorset, am ex tends ^thence along a broad valley to Worbarrow 

 Bay on the o^ er side of the Isle of Purbeck. At Swanage the 

 estimated thic]v ness of the formation is about 2300 feet, 3 but the 

 junction with tl ie Purbeck is not exposed. The lower beds consist 

 of variously coii our ed sands a*d c i avs re( i j yellow, grey, and 



