DRIFT-STAGES OF THP] DAKENT VALLEY. 



153 



Fig. 11. — Section on railway \ mile west of Dartford. 

 (l)ei)th of Section = about 30 feet.) 



W. E. 



b 



f. Trail of loam with Hints and flint-pebbles 1 to 2 feet 



h. Ochreous flint-gravel 



c. Broken ebalk. r'. Angular flint-rubble. 



a. Gravel composed chiefly of Tertiary pebbles "| 



j3. Yellow sand | 



y. Grey clay I 



h. White sand with land- and freshwater shells J 



1. fhanet Sands 4 to 5 



2. Chalk, with a festooned surface beneath the trail on 



the east side of the cutting. The indents are drawn, too deep. 



f. 



10 



The shells were Pisidium amnicum, Valvata piscinalis, Papa mar- 

 t/inata^ and a Succinea. Some fragments of bones were, I believe, 

 also met with. The bed/ corresponds with the well-known bed at 

 Erith, from which the late Mr. Grantham and Mr. E. Spurrell 

 obtained so large a collection of Mammalian remains. 



"We have here a definite horizon with which to correlate 

 several of the beds before described. There is little doubt that the 

 bed with elephant-remains at Shoreham and Eynsford corre- 

 sponds generally with /, fig. 11, and the height above the river of 

 the bed of gravel at the Otford brick-pit (g, fig. 10) agrees so closely 

 with the relative levels of the above that it affords grounds for 

 placing it in the same zone. The gravel 6, which belongs to the high- 

 level gravels of the Thames Valley, is older than /, and so there- 

 fore is the Limpsfield gravel-bed with which I would correlate it. 



This section also throws light upon a feature common in the 

 Chalk districts of Kent and Surrey, and which has yet failed to 

 meet with an explanation. I allude to that peculiar wavy break- 

 ing-up of the surface of the Chalk to the depth of 2 to 4 feet, in 

 the form of closely-packed, small spherical pockets with concentric 

 lines of clay and soil, which has been termed the " festooning of 

 the Chalk.'' 



On the western side of the cutting, the Low-level drift (/) abuts 

 against a steep low cliff of Chalk, and there is no festooned surface, 

 whereas on the eastern slope, where the Chalk has not been worn 

 back in the same way, the whole length of the slope exhibits, under 

 the thin covering of trail, the festooning as figured. In another 

 railway section, rather nearer to Crayford, the same bed,/, again 

 abuts against the Chalk, and overlies a mass of flint and Chalk 

 rubble ; and while under this bed the Chalk shows no festooning, 

 that portion of the Chalk slope which rises above it, and extends to 

 the top of the section, is strongly festooned. 



