part 1] SECTION AT WOKMS HEATH. 21 



can hardly be called a deposit) so commonly covering the higher 

 grounds of the Chalk-with-Flints ; for they give abundant evidence 

 of the occurrence of that material below Eocene beds, which has 

 only been occasionally noticed elsewhere, and then to a less extent. 



For the greater part, so far as I can see, this mass of unworn 

 flints in a loamy or clayey matrix, has been formed here by the 

 dissolving-away of the Chalk beneath the Eocene deposits, leaving- 

 behind the practically insoluble flints together with earthy matter, 

 reinforced perhaps from some Tertiary beds. But at what time 

 this process was started one cannot say ; it may have been in 

 Eocene times, directly after the deposition of the Blackheath Beds, 

 and it is possible that the dissolution of the Chalk may have begun 

 still earlier. As there is reason to think that the process is still 

 going on, we are faced with a thin mass of material, the formation 

 of which may have been going on slowly and more or less con- 

 tinuously for a long geologic time during which a great thickness 

 of Tertiary beds was laid down. 



The Clay- with- Flints therefore seems to be, not a deposit of 

 definite age, but a growth ; not part of our stratigraphic series, but 

 the residual product of a condition or state of things that has held, 

 in favourable circumstances, over long periods. As an illustration 

 from another branch of our science, it is in a somewhat like con- 

 dition to asbestos among minerals, that being, not a definite 

 mineral, but a condition of a certain class of minerals. Nature 

 sometimes declines to be definite. 



Occurrences of a like nature are to be expected with other lime- 

 stones than the Chalk. The most notable case known to me is 

 that of certain manganese-ores in the United States, which occur 

 in huge pipes and pockets in Silurian limestone. Unfortunately I 

 have lost the reference to them. 



It is interesting that the black coating so commonly found on 

 the flints in the outer part of the pipes of Clay-with-Flints is due 

 to manganese, and that Mr. G. M. Davies, who has kindly examined 

 specimens of the clays from Worms Heath, taken on a joint visit 

 in October 1918, finds that the grey clay which forms the lining of 

 the pipes owes its colour to a small amount of an oxide of man- 

 ganese. I had given a short note of his conclusions, but since I 

 wrote it he has written a full account of the matter, which follows. 



The few small green-coated flints found are, of course, sug- 

 gestive of the former presence of the base-bed of the Thanet Sand, 

 while a small mass of bright mottled clay, seen in the pit many 

 years ago, suggests the occurrence of a small included mass of 

 the Reading Beds among the pebbles. 



The evidence here therefore, as elsewhere, points to the Clay- 

 with-Flints being a residual product of the dissolution of the Chalk,, 

 reinforced by material from the old Tertiary beds. 



