6 J. L. LOBLEY CRETACEOUS BOOKS OF ENGLAND. 



the flood of waters which deposited at its mouth the "Wealden 

 formation. It has been, however, suggested that several rivers 

 of moderate or even of small size may have given origin to the 

 "Wealden deposits, even as off the coast of the island of Xew 

 Guinea a mass of sediment is now being formed by rivers, by no 

 means great, flowing fi-om Papua, which, though a large island, 

 can make no pretensions to continental dimensions. 



Remarkable in origin, the Wealden is remarkable also as a feature 

 of the England of to-day, since it forms the great valley, elevated 

 in the centre, bounded north and south and east by the Xorth and 

 South Downs, and opening out to the sea between Beechy Head 

 and Dover Cliffs. This great vale, of old covered with wood, as its 

 name indicates, is the tract of country known as the Weald, and 

 proverbial for picturesque beauty and exuberant fertility. The dip 

 of the Chalk forming the ranges of hills north and south is so 

 uniformly north and south respectively, and the underlying beds 

 crop out so regularly, that geologists can come to no other con- 

 clusion than that the entire area has been covered by Chalk of great 

 thickness, by Upper Greensand, by Gault, and by Lower Greensand, 

 also of great thickness, all of which groups of strata have been 

 swept away during successive ages by rain and rivers, or by the sea, 

 and that the North and South Downs are but the remnants of what 

 was once a vast sheet of Chalk continuous from the one range to the 

 other. The dome-like centre of this " valley of elevation " plainly 

 speaks of a great uprise, producing fractures of sufficient magnitude 

 to greatly facilitate the subsequent denudation of the surface rocks. 

 The Wealden formation also possesses consid(;rable interest from 

 the character of the organic remains found entombed in its beds. 

 The great reptiles [Iguanodon), forty or fifty feet in length, the 

 bones of which have been disinterred, doubtless lived on the banks 

 of the Wealden river or rivers, and gave after death their skeletons 

 to the stream, by the side of which they had probably tranquilly 

 died. At Brook Point, in the Isle of Wight, a mass of fossil 

 timber, once a raft of inland trees brought down to the Wealden 

 estuary and there stranded or sunk, strikingly illustrates the 

 conditions prevailing during the Wealden epoch. 



Lying upon the Wealden beds we find a great thickness of sands 

 containing a large amount of iron, with local beds of limestones and 

 clays, to which the name of Lower Greknsand was given, but now 

 frequently called the Neocomian. The name Greensand is so far 

 a misnomer that the bods of sand usually present to the eye a 

 reddish-brown colour. Sometimes, however, the green grains, from 

 the occurrence of which the beds obtained the name of Greensand, 

 are plainly observable. These green grains have been found from 

 microscopical examination to be the casts of minute creatures, of 

 which more will be said when the origin of the Chalk is spoken of. 

 Though green, these grains contain a large amount of iron, but in 

 the form of silicate, while the reddish-brown sands owe their colour 

 to the oxide of the metal. The Lower Greensand, though imme- 

 diately succcetling the Wealden, has had a markedly diff'erent origin. 



