LOWER GREENSAND. 47 



The strata dip gently (at about 2° to 3°) a little to the south of 

 west, and tlie green clay slopes down to the level of the rails in 

 the next cutting. The sands lying upon this clay are dark and 

 ferruginous, but are not well seen. 



The upper clay-bed, seen near Upper Hide, runs along the 

 valley in Apsecastle Wood, where it has caused a good deal of 

 slipping ; the lower clay-bed occurs at Apse Farm, but elsewhere is 

 overspread by a downwash of sand. 



The Ferruginous Sands between these localities and the liiver 

 Yar form an undulating tract, in part overspread with river-gravel, 

 but in part rising into flat-topped hills, capped Avith gravel. The 

 dip, if any exists, is too gentle to be detected in the small sections 

 that occur, except on Blackpan Common. 



The features of this tract suggest that the same beds which form 

 the escarpments of Pyle and Kingston, and of Godshill, extend 

 here across the valley of the Yar in a neck of about a mile in 

 breadth. The base line of the beds on the east side of the neck 

 seems to run from the cliff near Little Stairs Point, by the west of 

 Lake, past Borthwood, across the river near Alverstone, and thence 

 eastwards. The western boundary which we have already traced 

 through Godshill to near Branston, seems to be continued in the 

 hill on which Newchurch stands, and to trend thence eastwards, 

 but all evidence of its position is lost in the valley. 



Indicattons of Conditions under which the Lower 

 Greensand was deposited.^ 



" At the close of the deposition of the Wealden, there appears 

 to have been a sudden depression of the bed of the o-reat fresh- 

 water estuary, and an influx of the sea. The first effect of such 

 an influx would be the destruction of the animals in the estuary 

 not adapted for living in salt water ; hence we find a total de- 

 struction of the Wealden animals, the remains of which accumu- 

 late towards the point of the junction of that formation with the 

 Lower Greensand, — a fact which indicates the nature of the 

 change. Even the Gerithium [ Vicaryci], although belonging to a 

 genus many species of which are capable of living in the depths of 

 the sea, was destroyed, notwithstanding that its appearance, only 

 in the uppermost beds of the Wealden, indicates that its presence 

 there was due to the commencement of the very state of thino-s 

 which eventually destroyed it. That the depression was of some 

 extent, though not, perhaps, of very many fathoms, is indicated 

 by the nature of the animals which lived in the first-formed sea- 

 bed, and which, when they died, were often embedded in the fine 

 and probably fast-depositing mud, in the vertical position which it 



* Ou the Section between Blackgaug Chine and Atherfield Point, by Capt. L. L. 

 B. Ibbets-on and Prof. Edw. Forbes. I'roc. Geol. Soc, vol. iv. p. 409 (1844). 



