210 Domker — Junction of Chalk with Tertiary Beds. 



YII. — On the Junction of the Chalk with the Tertiaet Beds 



IN East Kent.^ 



By George Dowker, F.G.S. 



THE Junction of the Chalk with the Lower Tertiaries is nearly 

 always marked by the presence of green-coated flints ; and in 

 East Kent, where the Thanet Sands rest on the Chalk, numerous 

 junction-sections are exposed, exhibiting the peculiarities which I 

 now lay before you. 



Mr. Prestwich, in his paper on the Thanet Sands,^ speaking of 

 these green-coated flints, says, "A marked feature of that formation is 

 the constant occurrence at the base of the deposit, and immediately 

 reposing on the Chalk, of a layer of flints of all sizes, just as they 

 occur in the underlying Chalk, from which in fact they appear to 

 have been removed comparatively without wear or fracture, for they 

 are almost as perfect as the undisturbed flints, but present this dif- 

 ference, that instead of their usual white or black coating these 

 flints are almost invariably of a deep bright olive-green colour exter- 

 nally ; the white outer coating, which is often very thick, seems 

 removed (as though by an acid), and the flint then stained green. 

 So strong is the colour, although it forms a mere film, that flints 

 removed by denudation from this bed, subjected to great wear and 

 many changes, and imbedded in fresh beds, whether of the Tertiaries 

 or the Drift, can always be recognised by the peculiar green colour 

 which they invariably retain." These flints occur in East Kent, in 

 a bed of Sandy Clay of a dark ferruginous colour immediately on the 

 Chalk, passing upwards into a distinct Sand of a dark green colour, 

 varying in thickness from five or six inches to two or three feet, 

 though the Clay bed with the flints rarely exceeds five inches. It is 

 a matter of conjecture how far this Sand may belong to the Thanet, 

 or an intervening formation. It may generally be distinguished from 

 the lower beds of the Thanet in East Kent, which are very argil- 

 laceous ; but it is evident that the green-coated flints do not belong 

 to the Thanet beds, as they occur where this formation is absent.^ 

 Associated with this sand are found angular fragments of flint, 

 generally not more than one inch in width, remarkably sharp 

 and unrounded, though they appear to have undergone some 

 solution, their surfaces presenting a somewhat resinous look, in 

 other respects resembling the fragments of flint sometimes found in 

 the vertical fissues in the Chalk immediately below the Thanet Sand, 

 filled with tabular flint ; these fragments are not green-coated. 



Another peculiar feature of these j unction- secflons of Chalk and 

 Thanet Sand, as seen in East Kent, is that the green-coated flints 

 nearly always rest on a semi-tabular mass of Chalk flint,* which ex- 



^ See also Report of Proceedings of Geol. Soc, London, March 21, for two other 

 papers on similar subjects at p. 223. 



* Quart. Journ. Geol. Soc, Vol. viii., p. 243. 



3 See Prestmch, paper on "Woolwich and Reading Series. Quart. Journal of Geo- 

 logical Society, Vol. x., p, 95. Mr. "Whitaker in Geological Survey Memoirs, on 

 Sheet 13, and on Sheet 7. 



* See Mr. Whitaker's mper in Quart. Journ. Geol. Soc, Vol. xxi., p. 397. 



