Parr III. Sect. iii. § 2] CRETACEOUS. 817 
and (c) Dark clays with few fossils. 3. Upper Neocoimian (150 feet 
or more), consisting of (a) Cement beds with numerous fossils (Perna 
Mulletii, Exogyra sinuata, &c.); (b) Dark blue clays with Belemnites 
semicanaliculatus, &c. (c) Black clay with Belemnites; the top of the 
series not being seen. All these strata are covered unconformably by 
the Upper Cretaceous groups which successively repose directly upon 
all the horizons down to the Lower Lias. Owing partly to this circum- 
stance and partly to the thick covering of superficial deposits, no satis- 
factory sections are seen inland. In Lincolnshire, however, a portion of 
the Neocomian series comes to the surface from beneath the chalk, con- 
sisting of sands, sandstones, clays, and oolitic limestones, which, traced 
southwards by Tealby, pass into a group of calcareous beds (‘Tealby series). 
These strata contain Middle Neocomian fossils. Still further south they 
become white or brown nearly unfossiliferous sands and sandstones. 
Wealden.—In the southern counties a very distinct assemblage of 
strata is met with.’ It consists of a vast series of fluviatile or estuarine 
deposits termed the Wealden, from the Weald of Sussex and Kent where 
it is best developed, surmounted by a group of marine beds (“ Lower 
Greensand”), in which Upper Neocomian fossils occur. It would appear 
that the fresh-water conditions of deposit which began in the south of 
England towards the close of the Jurassic period, when the Purbeck beds 
were laid down, continued during the whole of the long interval marked 
by the Lower and Middle Neocomian formations, and only in Upper 
Neocomian times finally merged into ordinary marine sedimentation. 
The Wealden series has a. thickness of 1800 feet, and consists of the 
following subdivisions in descending order : 
Weald Clay. ; ; , : : : : - - 1000 fect 
Hastings Sand group composed of 
3. Tunbridge Wells Sand . : : : . 140 to 380 ,, 
2. Wadhurst Clay : : : : i EeOe | 180s. 
1. Ashdown Sand ; . F : : : . 400 or 500 ,, 
These strata precisely resemble the deposits of a modern delta. 
That such was really their origin is borne out by their organic re- 
mains, which include terrestrial plants (Equisetum, Sphenopteris, Aletho- 
pteris, Thuytes, cycads, and conifers), fresh-water shells (Unio, 10 
species ; Cyrena, 5 species; Cyclas, Paludina, Melania, &c.), with a few 
estuarine or marine forms as Ostrea and Mytilus, and ganoid fishes 
(Lepidotus) like the gar of American rivers. Among the spoils of the 
land floated down by the Wealden river were the carcases of huge 
deinosaurian reptiles (Iguanodon, Hylzosaurus, Megalosaurus, Vectisaurus, 
Hypsilophodon), long-necked plesiosaurs, and winged pterodactyles. The 
deltoid formation in which these remains occur extends in an east and 
west direction for at least 200 miles, and from north to south for at 
least 100. Hence the delta must have been not less than 20,000 square 
miles in area. It has been compared with that of the Quorra; in reality, 
however, its extent must have been greater than its present visible area, 
for it has suffered from denudation, and is to a large extent concealed 
under more recent formations. The river probably descended from the 
north-west, draining a vast area, of which the existing mountain groups 
1-On the wealden or fluviatile type consult, besides the works quoted on p. 814, 
Mantell’s Fossils of the South Downs, 4to, 1822; Topley, Geology of the Weald, in Mem. 
Geol. Surv. 8vo, 1875. 
G 
Sis) 
