WALTON COMMON EXPOSING LONDON CLAY ETC. 165 



permanent way. This is filled with bedded masses of fiint and flint- 

 pebble gravel, of a rich chocolate colour, which produce quite an 

 imposing effect when contrasted with the fine and pale-coloured 

 sediments of the underlying Eagshots. 



It is, however, between the second and third gaps that the contrast 

 of colour is the most marked. Here the hollows are filled with thick 

 courses of brick-red gravels, the stain of wdiich sometimes extends, 

 in varying tints of paler red, through a portion of the underlying 

 beds, until a line is reached where the percolation has been arrested. 

 Beneath such a line the Bagshot Sands look almost white by contrast. 

 When the section was fresh, these colours were reall)'' gorgeous, and 

 quite astonished the navvies. The fact is that the vicinity of the 

 third gap, at the western extremity of block D, marks the lowest 

 point of erosion of the Bagshot Beds, which continue to rise beyond 

 these limits. This part of the Plateau-gravel, therefore, must 

 represent a line of underground drainage, a circumstance which helps 

 to account for the accumulation of iron-pans towards the base : since 

 the more soluble matters, chiefly salts of iron in this case, are sure to 

 find their way to the bottom, and when a pan is once formed, the 

 coating of the pebbles above it continues to increase. 



The Plateau-gravel may be truly said to attain its maximum 

 development at the third gap, which almost coincides in position 

 with the boundary between Walton Common and Oatlands Park, 

 the latter commencing j ust where our section terminates. Deducting 

 a yard for " Top Sand," there must be 24: feet of gravel here. As 

 usual, pebbly gravels, more or less conforming to the eroded surface 

 and enclosing a certain proportion of false-bedded sand, fill up the 

 principal hollow. Some of the masses of sand here may be fragments 

 of the original beds, either torn off by currents or floated up by ice ; 

 but, if so, the structure has in most cases been considerably modified. 



At this point we may roughly divide the Plateau-gravel into three 

 vertical sections. The lower portion is such as I have endeavoured 

 partially to describe. The middle portion is more sandy, having 

 no doubt been largely derived from the Bagshot Beds of the adjacent 

 district, but also containing coarser material. It is often fairly well 

 bedded for short distances. The upper division is the most constant 

 throughout the entire area. It is usually the least bedded of the three, 

 has a greater proportion of large angular flints, cherts, tfcc. Sand 

 occurs in masses and pockets, and is sometimes rather argillaceous and 

 dirty, but always much coarser than the " soft sand " of the Bagshots. 

 If there is bedding it is often much twisted, so that the apparent 

 lines of stratification lie at all inclinations, and are sometimes 

 curved or contorted. It is not contended that these divisions are by 

 any means constant : but it is evident that the middle division is 

 largely expanded throughout block D ; and this circumstance helps 

 to account for the unusual thickness of the Plateau-gravel hereabouts. 

 The Metropolitan Convalescent Asylum (109 feet above 0. D.) is 

 220 yards from the end of the section on the south side of the line ; 

 and here a weU, said to be 30 feet deep, appears to have been sunk 

 entirely in the superficial beds. 



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