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Encyclopedia Britannica - Main :: WAT-WIL |
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WEALDEN , in geology, a thick series of estuarine and fresh-water deposits of Lower Cretaceous age, which derives its name from its development in the Weald of Kent and Sussex. In the type area it is exposed by the denudation of a broad anticlinal fold from which the higher Cretaceous beds have been removed. The Wealden rocks lie in the central part of this anticline between the escarpments of the North and South
Haslemere
Elland
coast
series . About Horsham the Weald Clay is moo ft. thick, but it decreases in an eastward direction; at Tunbridge it is cnly 600 ft. Certain subordinate beds within the Weald Clay have received distinctive names. " Horsham stone " is a calcareous flaggy sandstone, often ripple marked, usually less than 5 ft. thick, which occurs at about 120 ft. above the base of the Clay. " Sussex marble " is the name given to more than one of the high limestone beds which are mainly composed of a large form of Paludina (P. fluviorum); some of the lower limestone layers contain a small species (P. sussexiensis). The Sussex marble (proper) occurs about too ft. below the top of the clays; it is the most important of the limestone bands, and its thickness varies from 6 ft. to 2 in.; it is known also as Bethersden marble, Petworth marble, Laughton stone, &c. It has been widely used in the Weald district
The Hastings Sands are divisible into three main subdivisions: the Tunbridge Wells Sand, the Wadhurst Clay and the Ashdown Sand. Like the overlying Weald Clay this series thickens as a whole towards the west. In the west, the Tunbridge Wells Sand is separated into an upper and lower division by the thickening of a bed of claythe Grinstead Claywhich in the east
East
supply for the Wealden iron industry. Much of the higher portion of the Hastings Sand country is made of the Ashdown Sands, consisting of sand, soft sandstones and subordinate clay mends; in the east, however, clay is strongly developed at the base of this group, and at Fairlight is more than 36o ft. thick, while the sandy portion is only 15o ft. These clays with sandy layers are known as the Fairlight Clays. Beds of ignite are found in these beds, and a calcareous sandstone, called Tlgate stone, occurs near the top of the Ashdown Sands and in the Wadhurst Clay. The old town of Hastings is built on Ashdown Sand, but St Leonards is mainly on Tunbridge Wells Sand.Wealden beds occur on the southern side of the Isle of Wight and in the Isle of Purbeck in Dorsetshire. The Wealden anticline can he traced across the Channel into the Bas Boulonnais. A separate
The fossils of the Wealden beds comprise freshwater shellfish, Unio, Paludina, Melanopsis, Cyrena; and estuarine and marine WEALTH 437 forms such as Ostrea, Exogyra and Mytilus. An interesting series of dinosaurs and pterodactyles has been obtained from the Wealden of England and the continent of Europe, of which Iguanodon is the best knowna large number of almost entire skeletons of this genus were discovered in some buried Cretaceous valleys at Bernissart in Belgium; other forms are Heterosuchus, Ornithocheirus, Ornithopsis, Cimoliosaurus and Titanosaurus. Among the plant remains are Chara, Bennettites, Equisitiles, Fittonia, Sagenopteris and Thujites. The fishes, plants and reptiles of these formations possess a decidedly Jurassic aspect, and for this reason several authorities are in favour of retaining the Wealden rocks in that system, and the close relationship between this formation and the underlying Purbeckian, both in England and in Germany, tends to support this view. See CRETACEOUS, NEOCOMIAN, PURBECKIAN; also W. Topley, " Geology of the Weald," Mem. Geol. Survey (London, 1875). (J. A. H.) End of Article: WEALDEN If you wish, you can link directly to this article.
<a href="http://jcsm.org/StudyCenter/Encyclopedia/WAT_WIL/WEALDEN.html"> WEALDEN </a> |
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