568 MANUAL OF NATURAL HISTORY". 



IV. WEALDEN GROUP. 



The Wealden is a fresh- water deposit, consisting 

 of beds of clay, argillaceous limestones, and sands, 

 with occasional layers of lignite. It is considered 

 to be the delta of an ancient river, containing land 

 plants, fresh-water mollusks, fishes, tortoises, and 

 enormous saurians. 



In its geographical distribution this formation 

 extends from Horsham to Hastings, where it dips 

 beneath the sea, forms the bed of the English 

 channel, and re-appears in the valley of Braye in 

 the Department of the Boulonnois ; similar strata 

 occur in Germany and "Westphalia, in the Isle of 

 Bornholm, and at Niederschone in Saxony. 



In the Wealden formation an extinct genus be- 

 longing to the Order of Wading-Birds (Palceomis), 

 and a natatorial genus, the Cimoliornis, also ex- 

 tinct, have been detected. Large terrestrial and 

 aquatic reptiles abounded during the epoch of the 

 Wealden, among which may be mentioned the Igua- 

 nodon of Mantell, a gigantic, herbivorous saurian, 

 with serrated teeth, and which is calculated to have 

 attained the length of thirty feet ; there were also 

 the Hylceosaurus, with long, bony processes ar- 

 ranged along the back ; the Cetiosaurus, or Whale- 

 Lizard, with the spongy bones of a cetaceous ani- 

 mal, and of the size of the largest Whales ; the 

 Teleosaurus, or slender-nosed Crocodile, with the 

 tapering jaws of the Gangetic Gavial ; the Gonio- 

 pholis, or Swanage Crocodile, with angular plates 



