126 PROF. PRESTWICH ON THE AGE, FORMATION, AND 



11. On the Age, Formation, and Successive Drift-Stages of 

 the Valley of the Darent ; with Remarks on the Paljeolithic 

 Implements of the District, and on the Origin of its Chalk 

 EscARPaiENT. Ey Joseph Prestwich, D.C.L., P.R.S., P.G.S., &c. 

 (Read January 21, 1891.) 



[Plates YI., VII., & VIII.] 



Contents. 



Page 

 § 1. General Character and Age of Ibe Darent Valley 126 



2. The Chalk-Plateau Drifts and the associated Flint Implements. 128 



3. The Initial Stages of the Darent Valley 135 



4. The High-Le-vel or Limpsfield- Gravel Stage 137 



5. Contemporaneous Drift in the Cray Valley 144 



(5. The Brick-earths of the Darent Valley 145 



7. Other Drifts of the Darent Valley : the Chevening and Dunton- 



Green Gravel 147 



8. The Low-Level Valley-Gravels 151 



9. The Rubble on the Sides and in the Bed of the Valley 154 



10. The Alluvium and the associated Neolithic Implements 156 



11. On the Chalk Escarpment within the Darent District 156 



§ 1. General Character and Age of the Darent Valley*. 



In former papers t I have touched incidentally upon the drift phe- 

 nomena of this district, and on the occurrence of a peculiar group 

 of flint implements found on the adjacent Chalk plateau. I now 

 purpose to limit my observations to the circumscribed valley of the 

 Darent, which I have had more special opportunities of studying 

 since my residence at Shoreham. 



This valley, including the district surrounding it, is of peculiar 

 interest, from the circumstance that its geological history, beginning 

 with pre-Glacial times, may, with few breaks, be traced to Neo- 

 lithic times ; as also from the light it throws upon the age of 

 some of the Thames-Valley drifts, and from its distinctive groups of 

 Palaeolithic implements. It is moreover free from the complication 

 produced in the valleys north of the Thames by the presence of 

 foreign-drift elements, for here the drift is restricted to debris 

 derived from its own drainage-area. 



The Darent Valley is one of the few t which run through the 

 Chalk escarpment into the so-called Wealden area §, though it does 



* A general account of the drift-beds and denudation of this valley is given 

 by Mr. Topley in his 'Geology of the Weald,' pp. 188-194, and 270,' in Mem. 

 Geol. Survey (1875), to which I shall often have occasion to refer. See also 

 Messrs. Le Neve Foster and W. Topley 's ' Superficial De|30sits of the Valley of 

 tlie Medway, etc.,' Quart. Journ. Geol. Soc. vol. xxi. (1865) pp. 443-i74, and the 

 Maps of the Geological Survey. 



t Quart. Journ. Geol. Soc. vols. xlv. (1889) p. 270, and xlvi. (1890) p. 155. 



X Another of these valleys, that of the Wey, was described in 1851 by the 

 late R. A. C. Godwin-Austen in Quart. Journ. Geol. Soc. vol. vii. p. 278. 



§ Taking the Wealden area to mean physiographically the whole of the area 

 encircled by the escarpment of the Chalk. 



