BEACHES, ETC., OF THE SOUTH OF ENGLAND. 311 



the river-gravels and finally replaces them. Full details of the 

 section will be found in the paper referred to. The general section, 

 as I would interpret it, is given in PI. VII. fig. 3, and shows : — 



a. Eubble of unrolled and broken flints and chalk, with a few Tertiary pebbles, 

 red clay, and seams of sand. It contains land-shells {Pupa marginata, 

 Helix) with bones of the Mammoth, &e., resting on an uneven surface of — 



0. Eiver-gravel with mammalian remains {Elepkas, Equus, Bos). 



d. Flint gravel in red clay. 



The rubble {a) is in places roughly bedded, like the Brighton 

 Elephant Bed, in alternate seams of flints and rubble, while in other 

 places it is much disturbed and twisted, indicating great and 

 lateral thrust combined with a semi-fluid state. It contains no 

 Lower Greensand debris, and could not, therefore, as Col. Godwin- 

 Austen observes, have come through the gorge of the Wey, as the 

 river-drift has clearly done, but came, under glacial conditions, 

 from the Chalk Downs above and immediately south of the cutting. 

 Thence, also, it is evident the chalk and flints, with the red clay 

 and Tertiary pebbles, have been derived. 



At Peasemarsh, to the south of Guildford, another form of this 

 drift was described by E. A. C. Godwin-Austen^ as "an old ter- 

 restrial surface indicated by peat, trees, and sedimentary deposits." 

 A nearly perfect skeleton of a Mammoth was found there beneath 

 several feet of drift-gravel. At Wonersh Common the river-deposits 

 are buried under 5 to 8 feet of Lower Greensand debris, shed off 

 from the adjacent ridge. 



(8) The Thames Valley. — Some of the gravel on the slopes of the 

 hills and at low levels in the Thames basin may possibly have the 

 same origin — that is to say, it may be derived from adjacent older 

 and higher beds of gravel : such, for instance, as some of the 

 thin and irregular beds scattered over the lower plains skirting the 

 high and gravel-capped hills of Frimley, Chobham, and Ascot ; or 

 in similar positions in the main valley of the Thames ; or on some 

 higher slopes, as north of Burnham, where mammalian remains 

 have been found in a bed of brick-earth. I mention this merely 

 as a suggestion, for I have not been able to revisit the ground. 



These observations apply, however, only to a portion of the lower 

 gravels. Well-marked low-level river-gravels occur along the 

 Thames Yalley, though they are sometimes so mingled with this 

 later Rubble-drift that it becomes difficult to separate them. Or, 

 when this drift reposes on a Chalk surface, it may often be a 

 question whether the irregular surface of the Chalk results from 

 original erosion accompanying the deposition of the gravel, or is 

 due, as the gravel is so permeable, to subsequent solution of the 

 Chalk ; but when the underlying bed consists of clay, the irregu- 

 larity of the surface can have been caused only by the manner in 

 which the overlying gravel has been deposited. As an example of 

 the latter, we may take a section that was exposed on the Great 

 Western Hallway at Midgham near Newbury, in the tributary valley 



1 Quart. Journ. Geol. Soc. vol. vi. (1850) p. 90, and vol.xi. (1855) p. 112. 



Q. J. G. S. No. 190. Y 



