44 MK. H. W. MONCKTON^ Olf THE GRA.VELS SOUTH 03? 



deposits of hypothetical extra-morainic lakes near Warfield and 

 Finchampstead. If I rightly understand to what beds he refers, I 

 should say they are Bagshot Eeds, and in this view Mr. E. S. Herries 

 concurs. 



Irony concretions from the Bagshot Beds constantly occur in the 

 gravels of the Bagshot country, but it is not often that they can be 

 identified as casts of shells as in the instance already given. In 

 the pit in Lower Bagshot Sand, close to Easthampstead Church, 

 the sand is overlain by gravel full of these Bagshot concretions, 

 and amongst them I found a portion of a cast of a univalve, no 

 doubt a relic of the Middle Bagshot Beds which once existed 

 there. 



The derivation of the minor plateau- and terrace-gravels from the 

 gravel of higher plateaux in the immediate neighbourhood is par- 

 ticularly clear where two classes of plateau-gravel approach one 

 another. Thus, in fig. 1, p. 31, there is the gravel of Upper Hale 

 with very little chert, and that of the great plateau and Hartford 

 Bridge Mats with abundance of chert ; so the derivative gravel of 

 Miles Hill and the Fleet Pond plateau has little chert, for it was- 

 mainly derived from the Upper Hale gravel ; while the rest of the 

 terrace- and valley-gravels have abundance of chert, for they were 

 derived from Hartford Bridge Flats or from the great plateau. 



I have already described a similar example where the gravels 

 of the classes 2 and 3 of the Southern Drift approach one another 

 near Silchester, and we see the same thing in the Thames Yalley 

 near Eeading. I made a rough examination of a sample of smaller 

 material from the gravel-pit close to the mouth of the B-iver Kennet 

 and found it to consist of : — 



a. Subangular flints from the Chalk, Southern Drift, 



or older gravels 43 % of total weight. 



b. Chalk-pebbles and fragments from the Chalk ... 10 „ „ 



c. Flint-pebbles from Tertiary pebble- beds or older 



gravels 2 „ „ 



d. Quartz from Tertiary pebble-beds or older 



gravels 8 „ „ 



e. Quartzite-pebbles from the Glacial Gravel 1 „ „ 



/. Fragments of ironstone, fragments of fossils from 



the Oxford Clay or Oolitic rocks, possibly de- 

 rived from Glacial Gravel 17 ,, „ 



g. Bits of Osirea and other sliells in sandstone from 



the Tertiary Beds of Eeading 19 „ „ 



Amongst the larger material are many quartzites and fragments- 

 of old rock from the Glacial Gravel. Many of these stones have 

 originally come from a distance, but the whole of them may have 

 been derived for this gravel from the Chalk, Tertiary Beds, and 

 older gravels of the present drainage-area of the Thames, and in- 

 deed from the immediate neighbourhood. 



The Glacial Gravels are found in place at 314 feet above CD. on 

 the Tilehurst plateau, and at various levels up to 500 feet above O.D. 

 on the northern side of the Thames Yalley. N'ow, if the sea has 

 flowed in the Thames Yalley since these gravels were deposited, we 



