140 LOWER CHALK. 



Head to Southbourne, expose this bed at their base, and afford considerable 

 facility for its investigation. 



Near Lewes, the lower chalk occurs in the quarries at the foot of 

 Mailing Hill, Southerham, Glynd, Glyndbourne, Swanborough, Plumpton, 

 &c. ; and in other parts of the county, along the northern edge of the 

 Downs, reposing immediately on the grey chalk marl. 



The quarry at Southerham, (vide Tab. ii. fig. 3. and Tab. vii.) is re- 

 markable for the incUnation and direction of its beds; it is situated on the 

 east side of the road, on the south-western extremity of ChfF Hills. It 

 is about SO feet high, and contains from eight to ten layers of chalk, the 

 latter varying in thickness from one to eight feet, being separated from 

 each other by intervening seams of friable chalk marl. These exhibit decided 

 proofs of having suffered considerable displacement; they are incUned 

 obliquely towards the north, at an angle of from 20° to 30^, their planes 

 being depressed towards the west. Northward from this spot, at the 

 distance of about 300 yards, the upper chalk is exposed in the pit of 

 Messrs. Hillman, in South Street, and here the strata are horizontal. The 

 hill in which both these quarries occur, presents a smooth unbroken 

 outline, conveying no indication of the changes that have taken place be- 

 neath its surface ; hence we may infer, that the displacement of the strata 

 was antecedent to those revolutions, of which the present form of the 

 country affords such unequivocal evidence. 



Minerals. 



1. Sulphuret of iron is the only metallic substance that occurs in the 

 lower chalk ; and of this mineral some elegant crystals, of a reddish or 

 yellowish brown colour, have been discovered, in the quarries at the foot 

 of Mailing HiU. 



Tab. xvi. fig. 11, represents the usual form of the specimens. It con- 

 sists of nine or ten quadrangular columns, formed of octohedrons piled 

 upon each other ; these proceed from one common centre, and each ter- 

 minates in a quadrangular pyramid*. 



* Similar specimens have been discovered by Mr. Wm. Phillips, in the lower chalk at 

 Dover. Vide Geological Transactions, Vol. v. p. 37. 



