﻿490 MESSES. WHITE AND TREACHEE ON THE [Aug. I905, 



the hollow must be situated somewhere below the floor of the Lodge 

 pit. But the incoming of flint-bands, accompanied by a change in 

 the texture of the Chalk, near the visible base of Division (A) at that 

 spot, strongly suggests that the Phospbatic Series is there passing- 

 down into the normal Chalk shown in all the other sections in the 

 district. Unless appearances are deceptive, and an unconformity 

 actually occurs within the flinty beds lower down, the hypothesis of 

 the erosive origin of the trough must be rejected. 



(2) Turning to the second assumption — that the trough has a late, 

 or post- Cretaceous, tectonic origin — we may pass over (a) the sup- 

 position of faulting, as being neither supported nor opposed by a single 

 scrap of evidence, to consider (b) the possibility of synclinal folding. 



So far as we are aware, no undoubted instance of pre-Tertiary (in 

 this case, more strictly, pre-Reading) folding, save of the broad and 

 gentle type better described as regional warping, has yet been 

 recorded in the Chalk of the London Basin : but we attach little 

 value to this as an a-priori argument against the occurrence of such 

 at Taplow ; for until the Chalk of that area has been carefully zoned, 

 folds of insufficient strength to produce a distinct angular uncon- 

 formity between that formation and the Eocene, in the limited 

 junction-exposures usually available, are not likely to be detected. 

 The recognition of disturbances of this date in the Chalk of the 

 Hampshire Basin x and of Northern France, 2 and our own obser- 

 vations in Berkshire and Wiltshire, lead us to anticipate that the 

 mapping of the zones of the Upper Chalk will reveal the existence, 

 within the London Basin, of many flexures which either do not 

 affect the Eocene deposits, or affect them in a less degree. 



The evidence in favour of the synclinal origin of the Taplow 

 Phosphate-basin mainly rests on the inclination of the beds in the 

 Lodge section, and in the Root-House Pit, on the north. In the 

 former excavation this is approximately to the south-east, at angles 

 of 5° to 8° ; in the latter, to the south-south-east, or thereabouts, 

 at 6° to 8°. These dips are unusually high for the district, and, 

 so far as we have been able to ascertain, do not agree with 

 the inclination of the base of the Eocene deposits in the vicinity, 

 which appears to be a gentler one to the south-east. The crest- 

 line of the river-scarp, which practically coincides with the junction 

 of the Chalk and the Reading Beds on the west side of the Taplow 

 outlier, having a southward decline of about 1 j° between the two 

 excavations, the strong southern element in the much higher true 

 dip of the Chalk at the Root-House Pit, would, if persistent, 

 suffice to bring in a considerable thickness (not less than 100 feet) 



1 A. J. Jukes-Browne, 'Cretaceous Eocks of Britain' vol. iii, Mem. Geol. 

 Surv. 1904, p. 45 ; and C. Barrois, 'Recherches sur le Terrain Cretace Superieur 

 de l'Angleterre et de l'lrlande ' Mem. Soc. Geol. du Nord, vol. i (1876) 

 p. 113. 



2 See Marcel Bertram!, ' Sur la Continuity du Phenomene de Plissement dans 

 le Bassin de Paris' Bull. Soc. Geol. France, ser. 3, vol. xx (1892) p. 150; and 

 H. Parent, ' Notes supplementaires sur les Plis du Nord de l'Artois' Ann. Soc. 

 Geol. du Nord, vol. xxi (1893) pp. 102-104. 



