118 Dr. PiTTON on the Strata below the Chalk. 



very like chalk flint. In some specimens^ this dark variety adjoins, with 

 scarcely any gradation, a light grey, or white siliceous agglomerate, in which 

 the original sandy structure is still discernible ; while in the adjacent darker 

 chert the fracture is flat-conchoidal and splintery, with the glimmering lustre 

 of hornstone, all trace of the grains having disappeared ; — as if a sand of wax 

 had been consolidated by gentle softening, in a heat not sufficient for its 

 liquefaction. In its passage to chalcedony, the siliceous matter often assumes 

 a white colour, the aspect being nearly that of porcelain, and it becomes 

 translucent when moistened. 



(21.) A section of the upper part of this member (a) of the lower green- 

 sand, in the cliff about midway between Folkstone and Copt Point, was as 

 follows : 



Top of the Lower Green-sand. 



Feet. Inches. 

 Bluish grey clay (Gault), a few feet in thickness, at the top of the cliff: then — 



1. At the junction of the clay and sand is a bed consisting of pyrites in lumps, 



more or less decomposed ; about 1 



2. Grey quartzose sand, with numerous green particles 4 



3. Sand, in which lines of false stratification are conspicuous 1 6 



4. Similar, but coarser sand 2 6 



5. Sand, yellowish, slightly concreted, irregular in thickness ; much more solid in 



the eastern part of the clift' ; about 3 



6. Sand 2 



7. Irregular siliceous concretions 9 i 



8. Sand, nearly as above, with a few dispersed concretions 3 



9. Irregular concretions, like No. 7 1 6 



10. Sand, with a few scattered concretions 5 



1 1 . Irregular concretions, in sand ; more dispersed 2 



12. Sand, as above 4 



13. Concretions 3 to 6 



14. Sand ; as above, but finer ; about 5 



15. About four courses of concretions, with sand between 3 6 



1 6. Sand ; — to the foot of the cliff 4 



Total ; about 38 0* 



The concretions of Numbers 5, 7, 9, 11, 13, 15, consist of siliceous spongy 

 stone, like the whetstone of Devonshire, varying from a loose friable mass, to 

 the consistency of chert. In many instances the surface has the form of cylin- 

 drical stems. 



* The height of the cliff at this place is really not more than thirty feet ; but the proportions 

 are nearly as above given. 



