120 



THE POPULAR EDUCATOR. 



formed the escarpments which bound the weald, it is evident 

 that the foot of the chalk escarpment, as well as that of the 

 lower greensand, ought to be of the same level ; this, however, 

 is not the case. (2.) The escarpments follow the strike of the 

 beds, always changing their directions as the strike changes. 

 Now if the sea had beaten against the cliffs, it would not have 

 worn them away in one direction only, but would have cut 

 through the formation regardless of the strike. (3.) At the foot 

 of all sea-formed escarpments there must necessarily be a 

 beach, an accumulation of rounded pebbles caused by the action 

 of the waves rolling the detached pieces of the rock against 

 each other, but nothing of the kind has ever been discovered 

 at the edge of the weald ; and (4) if the country were at 

 present submerged so as to allow the sea again to cover the 

 weald, there would be such an arrangement of channels and 



reptiles, chiefly saurians, are not uncommon in this deposit. 

 The pterodactyl is here found, so also are many remains of 

 chelonians. 



The shells are of fresh-water origin, belonging to the genera 

 Melanopsis, Melania, Paludina, Cyrena, Cyclas, Unio. 



The Weald clay, upon which the Lower Greensand rests, 

 has the same mineral composition. This may be accounted for 

 upon the supposition that when the sea covered the delta of the 

 river which deposited the Wealden beds, the river was still 

 flowing and still carrying down the mud which formed the clay. 

 Now the same material from salt water gives rise to the Lower 

 Greensand. Occasionally bands of a limestone which is called 

 " Sussex marble " occur in the clay. This stone is almost 

 wholly composed of a species of Paludina. Shells of the crus- 

 tacean, the Cypris, are plentiful in the clay. 



islands as would preclude the possibility of the formation of 

 escarpments. There is no doubt that the weald has been denuded 

 by the simple action of rain and rivers ; for in the valley of -the 

 Medway river gravel is found at all levels. Without hesitation 

 any one would say that the Ayleaford gravel was the former 

 bed of the river now forty feet below; but similar gravel, 

 containing similar fossils, and placed by water flowing in the 

 same direction, is found here and there on the hill-sides, until 

 we are constrained to admit that the Medway once flowed 300 

 feet above its present level, and the river must have excavated 

 a valley some seven miles wide and 300 feet deep. If this can 

 be distinctly proved in the case of the basin of the Medway, we 

 may fairly conclude that the rest of the wealden area has been 

 denuded by the same means. 



The Hastings Sand is the lower division of the weald. 

 Notwithstanding its name, the division contains more argilla- 

 ceous strata than arenaceous : the whole attain a thickness of 

 some 750 feet. The " High rocks," and the steep cliffs which 

 give such picturesqueness to the scenery in the neighbourhood 

 of Tunbridge, belong to the Hastings sand. The remains of 



The Lower Greensand takes its name from the fact that 

 sometimes it contains green grains of the silicate of iron ; 

 occasionally they are so numerous as to impart a greenish tint 

 to the rock ; but the term " green " as a description is inap- 

 plicable. The general colour is dark brown, the sand being 

 often bound together by an abundance of oxide of iron, so much 

 so, indeed, that formerly the formation was known as " iron- 

 sand." The fossils it contains are marine, the most prominent 

 being Perna Mulleti (Fig. 123), a being part of the upper hinge ; 

 Ancyloceras gigas (Fig. 124) ; Nautilus plicatus (Fig. 125) ; Tri- 

 gonia caudata (Fig. 126); Diceras Lonsdallii (Fig. 127, a, b). 



The ancyloceras seems to be an ammonite more or less 

 uncurled. The Lower Cretaceous is sometimes called Neoco- 

 mian, because the formation is well developed near Neufchatel, 

 the Neocomum of the Romans. 



THE UPPER CRETACEOUS. 



The Gault. Although the Lower Greensand is sometimes 

 only separated from the upper by a thin bed of clay, yet a plain 

 line of demarcation runs between them, as may be gathered 



