THE THAMES FROM! GUILDFORD TO IS'EWBTJRT. 37 



There are several pits in this hill ; the gravel in that at the highest 

 point, 300 feet above O.D., is unstratified, but at the end above Amen 

 Corner, about 280 feet above O.D., it is very sandy, well stratified, 

 with current-bedding and over 11 feet thick. It is not easy to say 

 whether these patches of gravel with mnch chert from Windlesham 

 to Bearwood are contemporaneous or not, but I am inclined to think 

 that they are of much the same age as that of Hartford Bridge 

 Elats. 



I now pass on to gravels in Sheet XII. of the Geological Survey 

 map, of which no edition showing drift is as yet published, and I 

 therefore give a sketch-map (p. 38) to show the boundary of the 

 Southern Drift of Class 2. A line between the gravel with and 

 that without chert would run from the north-west towards the 

 south-east in an irregular manner quite regardless of the recent 

 river-system. Farley Hill, 260 to 270 feet above O.D., Heckfield 

 Heath, 270 'SGi above O.D., and Hazeley Heath, 270 to 288 feet 

 above O.D., are plateaux capped with very cherty gravel of the 

 Southern Drift, whilst Spencerwood Common, 230 feet above O.D., 

 and Eiseley Common, 152 feet above O.D., are also covered with 

 cherty gravel, and may be considered as valley gravels derived 

 from the Southern Drift. 



Such are the gravels with chert of Class 2. It may well be 

 that a river flowing from out of the Wealden area laid down the 

 gravels of the great Chobham Ridges plateau, and then cut its 

 channel westwards, the result being the gravels at lower levels of 

 Hartford Bridge Mats, Einchampstead Hidges, Hazeley Heath, 

 Heckfield Heath, and Farley Hill. 



Class 3. Silchester type. 



In this class I include a series of gravels which are distinguished 

 from Class 2 by an absence or great rarity of chert, and from both 

 Classes 1 and 2 by a great scarcity of small pebbles or fragments of 

 quartz. Farley Hill, Heckfield Heath, and Hazeley Heath are good 

 examples of the gravel with chert, and the plateau on a spur of 

 which Silchester stands is the type of a gravel without chert; 

 but between these places there are many hill- and valley-gravels 

 which form a sort of debatable land between the gravel with and 

 the gravel without chert. (See sketch-map, p. 38.) Spencerwood 

 Common, 230 feet above O.D., is capped by a gravel with chert 

 doubtless derived from the Farley Hill or Heckfield area. The 

 gravel-pit near Crosslane Farm, 1| mile IS'.E. of Mortimer Station, 

 190 feet above O.D., on the other hand, shows a gravel in which I 

 found no chert, so it must be derived from the Silchester side. 

 The hill 1^ mile S.W. of the same station, near Brick elton Farm, 

 appears to be capped by gravel without chert, and is therefore an 

 outlier of the Silchester plateau. 



There are extensive pits in a valley-gravel without chert at 

 Mattingiey 225 feet above O.D., and the hills between Hartley Wes- 

 pall and Eotherwick and at West Green are apparently capped by a 



