160 PROF. PRESTWICH ON THE AGE, FORMATION, AND 



EXPLANATION OF PLATES. 

 Plate VI. 



Sections. — The levels are taken from the Ordnance Maps, but in order to make 

 the sections clear the relations of heights to distances are made as .5:1, 

 so that the gradient of the Plateau-Drift is considerably exaggerated. 



Fig. 1. This section passes about ^ mile west of Broughton Hill, which is, 

 therefore, represented as in the distance, but the relative levels are 

 maintained. Broke Farm lies a short distance back of the number 

 480. Snag Lane is 2 miles lower down the valley of the Cray than 

 the point crossed here. 



Fig. 2. Extends from Oldbury to Yaldham along the line of watershed (now 

 removed in part) between the Darent and the Shode. Ash lies a 

 little to the east of the line of section between South Ash and West 

 Yoke. The brick-earth and gravel, e, with Mammalian remains and 

 Palaeolithic implements (0), north of Milton Street, lies a short 

 distance east of the line of section, but on the level here represented. 



Fig. 3. In this section it will be seen that the Lower Greensand debris 

 (Southern Drift) and the Palieolithic implements (v) are of frequent 

 occurrence on the highest summits of the escarpment. The dotted 

 line above e across the Valley of the Darent gives the level of the 

 Limpsfield drift at the adjacent Broughton Hill. The dotted line 

 ran follows the base-line of the escarpment — the summit-level at 

 Limpsfield being near I and at Yaldham at V . 



Plate VII. 



Map. — This is based essentially on the Oeological-Survey Maps, with the ex- 

 ception that the Drift-beds are altered and added to in accordance 

 with the interpretation given to them in this paper. The angular 

 gravel, h, should probably have greater extension. The Sundridge and 

 Brastead gravels, of which I have never as yet been able to see a section, 

 should possibly be referred to the same zone. It also covers more 

 ground about Seal and below Seal Chart. The Southern Drift is 

 taken as co-equal with the Red Clay-with -flints. The names of 

 places generally indicate the position of their churches. 



In the drawing of this map I have been much indebted to the kind 

 assistance and suggestions of Mr. Topley. 



Plate VIII. 



These sketches, made by Mr. W. S. Tomkin, represent some of the more common 

 forms of the Plateau-Implements. Figs. 1 to 6 will be found described 

 in the text, p. 134. Fig. 7 is an exceptionally good instance of the 

 scratches or strias, closely resembling glacial striae, which are not 

 infrequent on the brown-stained flints. In this case the large mis- 

 shapen flint seems to have been trimmed at the edges so as to form a 

 rude cutting instrument or adze. 



In consequence of the uniform brown colour which spreads alike over the 

 natural and the worked surfaces of the flints, independently of the original 

 colour, the distinction between the two surfaces is rendered less apparent than 

 is shown in the drawings, where the originally darker natural surfaces alone 

 are shaded, while the colour on the worked edges is not rendered. Added to 

 this the wear and abrasion which have affected the whole flint, including the 

 trimmed parts, are not made sufficiently apparent. These parts, therefore, show 

 more prominently than in the specimens themselves. The figures in Q. J. G. S. 

 vol. xlv. pi. X. exhibit this feature better, though the general drawing is not so 

 good. 



