part 1] DEPOSITS AT WORMS HEATH. 27 



It will be seen that the material from Worms Heath corresponds 

 very closely in composition with halloysite, and may be represented 

 by the formula Al a O, . 2Si0 2 . 2H a O. + Aq. This is the formula of 

 halloysite, while without the water it would serve for kaolinite. 

 Allophane corresponds to the formula A1,0, . Si0 2 . 5H 2 0, or to 

 A1 2 0, . Si0 2 . 6H,0. The molecular ratio of silica to alumina in 

 allophane is as 1:1, not 2 : 1 as in halloysite and kaolinite, and 

 there is more combined water. 



Mr. Edge remarks that the material, when shaken up with water, 

 yields a suspension which readily passes through filter-paper. 

 He thinks that it corresponds to the ■ kaolin jelly ' of E. Ramann, 1 

 and may have been washed through the sand as a dilute colloid 

 and held up on reaching the clay which lines the pipes. 



Conclusions. 



A study of the materials filling the pipes, and of the exposures 

 .at Worms Heath, suggests the following sequence of events. By 

 •early Eocene times the Chalk had become consolidated, and most of 

 its silica had segregated to form nodules of flint, while manganese 

 was distributed in the form of small dendritic growths. The 

 ■cor-anguinum and higher zones had been eroded by wave-action, 

 when the Chalk sank far enough beneath the Eocene sea to be 

 protected from further attrition. Solution, however, took place 

 either on the sea-floor or beneath a light deposit of sand, and the 

 residual flints acquired a green coating and formed such a bull-head 

 bed as is usually seen at the junction of the Chalk with the Eocene. 

 It is doubtful whether the green coating can be formed, except in 

 contact with sea-water. Subaerial solution of the Chalk may 

 give rise to black-coated flints, but descending meteoric waters are 

 in general too deficient in potash to form green glauconitic or 

 ■celadonitic products. The sands at Worms Heath contain no 

 glauconite and very little felspar, and the small amount of muscovite 

 present cannot have yielded much potash. 



The Chalk with its bullhead bed was covered in succession by 

 the sand, the pebble-bed, and probably by the London Clay and 

 other Eocene deposits. Then followed emergence and subaerial 

 -erosion of the overlying beds. Water from the pyritiferous London 

 Clay may have brought the iron that stained the pebble-beds 

 brilliant shades of red, and that formed the masses of iron-sandstone 

 ■and conglomerate. Comparatively little of the unaltered buff- 

 coloured sand-and-pebble bed is left. 



The formation of pipes of such size and depth must be due to a 

 considerable volume of surface-drainage from the London Clay 

 area, which sank into swallow-holes on reaching the permeable 

 Blackheath pebbles and sands. Passing through these, the water 

 •encountered the Chalk and began to dissolve it, leaving behind the 

 insoluble flints and brown clay, and at first also the more robust 



1 ' Bodenkunde ' Berlin, 3rd ed. (1911) p. 245. 



