152 PROF. PRESTWICH ON THE AGE, FORMATION, AND 



\ 



flints, and some Tertiary flint-pebbles. A few of the pieces of 

 Chert are of the variety known as " Oldbury Stone." The 

 sandy matrix is of Lower-Greensand origin. K^o organic remains 

 and no Palaeolithic implements have hitherto been found in this 

 pit. The surface of the underlying Gault is nearly level. 



The gravel has all the appearance of a river-drift formed at the 

 junction of the east and west branches of the Darent Yalley, and 

 whether or not it is a stage newer than the Chevening and Dunton- 

 Green gravel it would be difiicult to say. The difl'erence of level, 

 though slight, the unstratified condition of one drift, and the rough 

 bedding of the other, point to a difference of origin and time. The 

 surface of the gravel at the Otford jnt is slightly contorted as though 

 by the action of river-ice, as at St. Acheul, in the valley of the 

 Somme, though it is here less apparent and on a much smaller 

 scale. I know of no similar bed in the western branch of the 

 valley, unless it be connected with the small drift deposit of brick- 

 earth and gravel at Proghole Parm near Chipstead. In the eastern 

 branch, the small outlier at Child's Bridge * is of the same age. 



North of Otford, no beds of gravel are to be seen for some miles 

 down the valley, but in laying a drain on the west side of the 

 valley near the paper-mill at Shoreham a thin bed of sand and 

 gravel, consisting of flints with worn fragments of Chert and Rag- 

 stone, was discovered beneath the surface-soil. In this the tusk 

 of a IMammoth was found, with traces of land- and fluviatile shellsf. 

 It was 30 feet above the level of the river ; and at about the 

 same level and under similar circumstances a tooth of the Mammoth 

 was obtained at Eynsford. These are the only two instances in 

 which organic remains have been found in the Valley of the Darent, 

 though so common in the adjacent valleys of the Medway and 

 Thames. A considerable spread of gravel on a low level is shown 

 on the Geological-Survey maps in the valley between LuUingstone 

 and Eynsford, but there are no pits or sections. 



At the junction of the Darent with the Thames Yalley, some 

 sections of considerable interest were exposed on either side of 

 Dartford during the making of the North-Kent Railway in 1842. 

 On the Stone or east side, the line passed through a thick bed 

 of gravel (15 to 20 feet), regularly bedded, and reposing upon a 

 nearly level surface of Chalk (cmte, p. 144). I am not aware that 

 any fossils were found in it, and Palaeolithic implements were then 

 unknown and unsought for. It belongs to the great stream 

 of gravel of the old Thames, but it shows the influence of the 

 Darent-Y alley stream in the large amount of Lower-Greensand 

 debris there present. 



On the west of Dartford there are two short cuttings between 

 the Darent and the Cray, of considerable importance in their 

 bearing on this enquiry. The one adjoining the Darent Yalley, 

 and at right angles to it, is as follows (fig. 11) : — 



* Quart. Journ. Geol. Soc. vol. xlv. (1889) pp. 274, 285. 

 t Geol. Mag. dec. iii. vol. vi. p. 113. 



