CHAPTER XVIII.

WEALDEN GROUP.

The Wealden divisible into Weald Clay, Hastings Sand, and Purbeck Beds--Intercalated between two marine formations--Weald clay and Cypris-bearing strata--Iguanodon--Hastings sands--Fossil fish--Strata formed in shallow water--Brackish water-beds--Upper, middle, and lower Purbeck--Alternations of brackish water, freshwater, and land--Dirt-bed, or ancient soil--Distinct species of fossils in each subdivision of the Wealden--Lapse of time implied--Plants and insects of Wealden--Geographical extent of Wealden--Its relation to the cretaceous and oolitic periods--Movements in the earth's crust to which it owed its origin and submergence 225