GEOLOGY 



folds we find higher Cretaceous deposits coming on in succession above 

 the Weald Clay in the southern part of the county between Eastbourne 

 and Midhurst. The earliest of these strata belongs undoubtedly to the 

 Lower Cretaceous period ; for this Atherfield Clay, so called from the 

 place where it is best seen, Atherfield in the Isle of Wight, contains 

 Lower Greensand marine fossils. The Atherfield Clay has only been 

 traced as far east as Warminghurst, where Mr. Lamplugh recently 

 noticed about 20 feet of clay with marine fossils, below the sandy Hythe 

 Beds, and resting with a sharp division on the blue shaly Weald Clay. 

 It is by no means clear yet whether there is not everywhere a break 

 between the Atherfield Clay and the Weald Clay below ; for there is 

 a sudden change from estuarine to purely marine conditions, and near 

 Eastbourne most of the Lower Greensand and probably much of the 

 Weald Clay have been cut out or overlapped by deposits of somewhat 

 newer date. Unfortunately however the junction of the two clay deposits 

 is difficult to examine ; for it usually occurs in flat land where natural 

 sections are wanting and artificial sections are scarce. Wells are not 

 sunk, near the junction, for there is seldom any water to be had, and that 

 found is not palatable. 



The Lower Greensand above the Atherfield Clay consists mainly of 

 sandy deposits with subordinate beds of harder rock. When met with in 

 wells or excavations some depth below the level of the surface, the sands 

 are commonly tinged more or less with green (hence the name ' Green- 

 sand ') from the presence of small grains of a dark green mineral known 

 as glauconite. This mineral, which is an iron compound, readily oxidizes 

 on exposure, and then the sands take the familiar bulf or rusty hue which 

 makes people wonder why geologists ever called them Greensand. There 

 is a remarkable change in the Lower Greensand when traced from west 

 to east and south through Sussex. At Petersfield it has a thickness, 

 according to Topley, of 425 feet ; seventeen miles to the east, at Pul- 

 borough, it has decreased to 380 feet, through the thinning of the 

 two lower divisions, the Atherfield Clay and the Hythe Beds. Another 

 seventeen miles to the east, at Hassocks Gate, the total is only 130 feet, 

 the Atherfield Clay having disappeared and the other three divisions 

 having thinned considerably. Five miles or so further towards the 

 south-east the bold pine-clad sandy ridges which characterize this forma- 

 tion sink and seem to melt away into an almost featureless undulating 

 plain, which stretches to the sea near Eastbourne, where the Lower 

 Greensand is represented by a few feet of coarse sand between the Gault 

 and the Weald Clay, all the rest of the formation having disappeared. 

 The question of the relation of the Lower Greensand to the Wealden 

 strata in Sussex happens to be of more than purely scientific interest ; 

 for if Lower Cretaceous deposits can disappear so rapidly towards the 

 south-east, it is evidently possible that the geological structure may cor- 

 respond with that on the northern side of the Wealden anticline, and the 

 Lower Cretaceous and perhaps the Jurassic strata may be entirely wanting 

 around Newhaven. Palaeozoic rocks may there occur much nearer to 



7 



