456 T. E. JONES AND C. C. KING ON SOME 



into further west. This would probably be at about the same time ; 

 and beyond Section No. 4 it was removed entirely, nothing being 

 left but small seams of clay and clay-galls in the yellow sands, as 

 seen in Sections JNos. 2, 1, and 6. We cannot suggest any more 

 definite direction for the cliff or bank, than that possibly it was 

 about N.-S. in accordance with the position of the apparently abrupt 

 ending of the grey clays, between Sections Nos. 4 and 3 : see the 

 Plan of the Pit, fig. 3. This line would also agree with the local 

 absence of Oysters at Section No. 3, and at Castle Kiln. 



It is possible that there then existed other and distinct clay-beds, 

 some even as dense and homogeneous as the present "Mottled 

 Clay," of which some of these rounded lumps are the sole remnants. 

 This goes to prove the greater complication of processes in the forma- 

 tion of the " Reading Tertiaries," and adds to the length of time 

 required for them. In any case, not only does the rolling of the 

 clay-galls bespeak a flat shore and neighbouring cliff, but their 

 enclosed flints clearly indicate a beach, bank, or shoal of flint debris 

 at no great distance, whether in fresh, brackish, or salt water*. In 

 a section at Red Hill, 7£ miles "W. of Heading, Mr. Prestwich {op. 

 cit. p. 87) observed a "patch of angular chalk fragments, sub- 

 angular flints, and flint pebbles " just above the yellow sands ; and 

 these, though rather higher in the series, were probably derived 

 from a similar, if not the same, beach or shoal. 



The scattered subangular flints and the occasional pebbles of 

 lydite in the other derivative seams of clay and clay-galls, at a 

 lower level, have also their own significance ; and the green-coated 

 flint in Section No. 2 shows that the " Bottom-bed " itself, or the 

 nearly contemporaneous "Thanet Sand," was somewhere already 

 exposed to denudation while the shallow-water and false-bedded 

 yellow sands were being deposited. 



EXPLANATION OF PLATE XXII. 



Illustrative of Sections of the " Woolwich and Reading " Tertiary Beds at 

 Coley Hill, Reading, Berks. 



Fig. 1. Diagram of a river eating away its banks and forming shoals.. 



2. Diagram of the destruction of a clay bank, and the deposition of rolled 



lumps of clays, at two successive periods. 



3. Diagrammatic plan of Collier's Pit, Coley Hill, showing the relative 



* As to the conditions of deposit, we see that the Marine " Bottom-bed " was 

 succeeded by the shallow-water, perhaps estuarine, sands, and leaf-beds (some 

 shell-beds with Ostrea hold this position in the London district), and these by 

 the Mottled Clay, deposited, quickly perhaps, over a large area of quiet water 

 invaded by mud inimical to life. To this area the sea, again, brought Oysters, 

 as shown by the Shell-beds with Cerithium, Cyrena, and Ostrea, lying on the 

 Plastic Clay at Guildford, 20 miles to the S.E., and at Croydon, nearly 40 miles 

 to the E. by S. of Reading. These estuarine Oyster-beds, together with the 

 marine Oldhaven series, if they existed here, were denuded off the clay in the 

 Reading district before the Basement- bed of the London Clay was laid down. 

 See also W. Whitaker " On the Lower London Tertiaries," Quart. Journ. Geol. 

 Soc. vol. xxii. p. 409, pi. 22; and for the extension of these beds into France, 

 &c, Prestwich, ibid. vol. xi. p. 213 &c, pi. 8. 



