Page:VCH Kent 1.djvu/74

 A HISTORY OF KENT Four other Kentish Borings,' viz. : — IV. Ottinge V. HoTHFiELD VI. Old Soar V^II. Penshurst lo miles 3 miles 5 miles (Ensfield) Formation west of N.W. of N.N.E. of 3 miles west of Dover Ashford Tonbridge Tonbridge Lower Greensand and) ^, a f» .o^f» , r„ h /f Atherfield Clay . .} ^^^ ^'- '^^^'-^ 5o ft.(?) Wealden and Purbeck 146 „+ 593 „ + 650,, + 1511 ft. Kimeridge Clay .. — — — 356,,+ These coal-exploration borings do not however exhaust our informa- tion as to the deep-seated rocks of Kent. In the north-west of the county two borings for other purposes had previously reached strata older than any at the surface. These were as follows : VIII. Boring at Crossness near Erith ^ System Formation Thickness in feet Pleistocene . . Alluvium, Valley Drift, etc 39 Lower Eocene . Lower London Tertiaries 98 r, n . i Chalk 696 (?) Upper Cretaceous i ^ , 7 / '^'^ I Gault 175 i^'t^  } Red Marls and Sandstones (of doubtful age) . 52 (or Devonian) J ^ b / j . Total . . . i,c6o XL Boring at Chatham Dockyard^ System Formation Thickness in feet Pleistocene . . Valley Drift, etc  Lower Eocene . Lower London Tertiaries / ' Upper Cretaceous i r^ , "^"^ ^ Gault 193 Lower Cretaceous Lower Greensand 41 Upper Jurassic • Oxford Clay 22 Total. . . 965 We will now briefly discuss the fresh discoveries represented by the above records and indicate their principal bearings, referring the reader to the literature mentioned in foregoing footnotes for fuller information. The first point which deserves attention is the surprising variety of the older divisions of the Secondary rocks both in character and in thickness, and the diversity of the underlying Palsozoic formations. The rapid changes in the underground stratigraphy thus indicated are in striking con- trast with the simplicity and regularity of the surface geology of the 1 Recorded by Prof Boyd Dawkins, Refott British Assoc, for 1899, p. 737. Borings have also been made at Pluckley, 6 miles west of Ashford, and at a site between Ropersole and Dover, but the records have not yet been published. 2 See Prof J. Prestwich, Quart. Joum. Geol. Soc. (1878), xxxiv. 902 ; also W. Whitaker, 'Geology of London ' (1889), i. 19, ii. 66. 3 See W. Whitaker, Quart. Journ. Geol. Soc. (1886), xlii. 26, and 'Geology of London,'!. 27. Also ' The Deep-seated Geology of the Rochester District ' (Presidential Address), Trans. South-Eastern Union of Scientific Socs.for 1899. 28