164 MK. W. H. HUDLESTON ON A SECTION THKOUGH 



commencenieiit. They have been deeply eroded, and are cut down 

 to the level of the line, and even slightly below it in three places, 

 which may be called respectively No. 1 gap, No. 2 gap, No. 3 gap, 

 going from east to west. The lithology here is of the usual character, 

 a fine and equally grained " soft sand," faint yellow to buJ0P, and 

 even brownish or reddish at top, where much percolated. Slight clay 

 laminations occur throughout, helping to show the bedding, which 

 is pretty regular and current-bedded only for short distances. The 

 colour-banding, as distinct from the bedding, follows the curves of 

 the eroded surface, showing clearly that the reds are due to infiltra- 

 tion from above. This is, perhaps, better seen beneath the shallow 

 basins than in those more deeply excavated. The average thickness 

 of the Bagshots exposed in block D, may be taken at about 7 feet. 



The Plateau-gravel of Block D. — Assuming the cutting to be about 

 26 feet deep here, a thickness of about 19 feet must be assigned as 

 the average of the superficial beds ; whilst, as we have seen, in some 

 places they occupy the entire depth of the cutting. No. 1 gap is 

 about 9 yards across. On the east side the " Blue Bagshots " are cut 

 sharply off, and the superficial deposits in the bottom of the cavity 

 conform, more or less, to the sides, which are lined with a layer of 

 mixed flints and pebbles holding uj) a mass of reconstructed sand 

 about 4 ft. thick, overlain by other masses of reconstructed sand with 

 pebbles, showing a different stratification. 



Such masses of sand are often disposed in nearly horizontal layers, 

 between which much current-bedding is exhibited. At first, from 

 their external resemblance to the Bagshot Sands in situ, I mistook 

 them for these beds, fancying that tongues of gravel had been 

 thrust between the divisional planes, or even in some instances that 

 masses had been transported bodily. I think it is quite probable 

 that in some cases my former interpretation may be the correct one ; 

 but, in a majority of instances, a close examination of the sands in 

 the Plateau-gravel will show that they are coarser, more unequal 

 in grain, and devoid of the clay laminations so characteristic of the 

 beds on which they repose. Although the material is mainly the 

 same, the one has been a turbulent, the other a comparatively quiet 

 deposit. That section of the Plateau-gravel which lies between the 

 first and second gaps consists, especially in the lower, though not 

 quite the lowest parts, of immense masses of this kind of sand, which 

 are often somewhat ferruginous. 



Even here the actual base of the Plateau-gravel is for the most part 

 occupied by beds in which the regular Tertiary flint pebble is largely 

 rej)resented. These gravels present a sort of rude stratification, 

 especially conformable to the shallower depressions of the Bagshot 

 surface, which, as a rule, they fill up in a series of concentric layers, 

 sometimes loose, more often cemented by deep brick-red iron-oxide, 

 with here and there a streak of black oxide of manganese above. 

 Under these circumstances there is do difficulty in drawing the line 

 between the Bagshot Sand and the Plateau-gravel : the contrast, in 

 fact, is exceedingly sharp. The hollow about halfway between the 

 first and second gaps is cut down to within three or four feet of the 



