

CHAP. X.] CRETACEOUS PERIOD. 165 



near Cuckfield and Lindfield there are thin layers of con- 

 glomerate, the pebbles in which are largely derived from 

 Palaeozoic rocks, and were probably brought down by 

 streams draining off the land to the north ; and this is in- 

 teresting as showing that streams had already cut down 

 through the Upper Jurassic clays to the Palaeozoic rocks of 

 that region. The Weald Clay consists of clays and shales 

 with local beds of sandstone and many layers of shelly 

 limestone, the latter consisting of Paludina shells, and re- 

 sembling the Upper Purbeck limestones. 



The Wealden Beds are about 1,800 feet thick in the west 

 of Sussex, and they attain a still greater thickness near 

 Swanage in Dorset ; but when followed westward they are 

 found to thin out rapidly, being only 172 feet thick in Man- 

 of-War Cove. In Dorset, moreover, the series is not divi- 

 sible into a lower sandy and an upper clayey portion, the 

 sands and clays alternating throughout, but the highest 

 beds are always shales with limestone bands. 



The fossils of the Wealden are entirely freshwater and 

 terrestrial, plant remains, minute Crustacea, freshwater 

 mollusca, fish and reptile bones occurring throughout ; and 

 there is no admixture of marine species, except at the very 

 top of the series in the Isle of Wight. 



Wealden Beds occur in the Vale of Wardour, but are 

 not seen again in Wiltshire. In Oxfordshire there are 

 some freshwater deposits overlying the so-called Purbeck 

 Beds, but there is a decided unconformity between them, 

 and just as the one group in all probability antedated the 

 true Purbeck Beds, so it is thought that the newer group 

 is of posterior date to the true Wealden series. 



In Yorkshire and Lincolnshire there are contemporary 

 beds of marine origin. In Yorkshire these are blue clays 

 with a basement bed containing rolled fossils derived from 

 Jurassic rocks ; in Lincolnshire they are partly clays and 

 partly sandstones, with a similar nodule-bed at the base ; 



