40 MK. H. W. MONCKTON ON THE GKAVELS SOUTH OP 



of this long ridge attains a height of over 500 feet at the old 

 camp called Grimsbury Castle, and there is a small pit at the fork 

 of the road 5 furlongs south of the " Castle." Subangular flints, 

 very much worn, broken, and decayed, and flint-pebbles form 

 nearly the whole of the gravel. There are a few fragments of 

 flinty sarsen similar to that which I noticed on the Silchester 

 plateau. 



The next gravel-capped hills to the west are Snelsmere East 

 Common and Snelsmere Common, but it is not proposed to include 

 them in the present paper. My survey of the Southern Drift is, 

 therefore, now completed. It will be seen that I have followed 

 Prof. Prestwich pretty closely/ though I have ventured to include 

 in the Southern Drift the gravels at several localities which he does 

 not mention. 



II. The Westletok Shingle. 



This is the Pebble Gravel of the Geological Survey map. Its 

 classification with the shingle at Sonthwold and Westleton was, I 

 believe, first suggested in print by Mr. Whitaker in his ' Guide to 

 the Geology of London,' 3rd ed. (1880) p. 57. 



Bowsey Hill, 467 feet above O.D., and Ashley Hill, over 400 feet 

 above O.D., close to it, are capped by this gravel. There are a good 

 many subangular flints, but it consists mainly of flint and quartz- 

 pebbles, and is very different from the Southern Drift above 

 described at Coppid Beech Lane, 300 feet above O.D., and 7^ miles 

 to the south. If, as Prof. Prestwich thinks, the Southern Drift 

 now at the lower level is the older of the two, great northerly eleva- 

 tion must have taken place since both were deposited. 



III. Glacial Geavels. 



The Tilehurst plateau, 290 to 341 feet above O.D.,^ between the 

 Rivers Kennet and Thames, a little west of Beading, is in my 

 opinion capped by an outlier of the great stretch of Glacial Gravel 

 which extends northwards from Caversham on the opposits side of 

 the Thames. I base my opinion that this is Glacial Gravel on its 

 character as a plateau-gravel, taken together with its composition, in 

 which it differs greatly from the other classes of gravel; thus 

 pebbles of red quartzite, weighing over | lb., are abundant. I also 

 think that when the gravel was formed the present valley of the 

 Thames above Beading cannot have been in existence. The reader 

 will probably agree that this gravel is not older than the climax of 

 the Glacial Period, and, as the valley through which the Thames 

 flows above Beading is now about 160 feet deep, one can form 

 some idea of the amount of denudation which has taken place since 

 that time.^ 



^ See his account of the district, o-p. cit. pp. 159-162. 

 2 See O. A. Shrubsole, ihid. p. 589, § 2, Norcot Brickyard. 

 2 Cf. Prestwich, ibid. p. 149, fig. 13. 



