VALLEY AND ITS EELATION TO THE WESTLETON BEDS, ETC. 179 



5. That none of the valleys on the north side of the Thames Tertiary 



Basin date back beyond the Pre-Glacial epoch, and that the 

 whole of the valley-system of that area is of later date. 



6. That the escarpment of the Chalk, and probably that of the 



Oolites, in the Midland Counties, is of a more recent date than 

 the Westleton Shingle, and therefore not older than late Pre- 

 Glacial or early Glacial. 



7. That there is a Southern Drift as vs^ell as a Northern Drift in 



the Thames Basin : and that this Southern Drift has been 

 derived from the Lower Greensand of the Wealden area and 

 from the Chalk and Tertiary strata formerly extending over 

 portions of that area and the adjacent downs. 



8. That during the early Pliocene (Diestian) epoch the Wealden 



area was partly or wholly submerged, and that a continuous 

 sea extended thence over certain portions of Prance and Bel- 

 gium, while the present Strait of Dover was non-existent. 



9. That subsequently to this period, but before the in -setting of 



the Glacial period, the AVealden area and the Boulonnais 

 underwent an upheaval, resulting in the formation of an anti- 

 clinal range 2000 or 3000 feet high. 



10. That it was from the slopes of this anticlinal that the materials 

 composing the Southern Drift were derived, and spread over 

 the area now forming the southern side of the Thames Basin. 



Tl. That this denuding action commenced at the time of the Red 

 Crag, and was continued uninterruptedly through several 

 successive geological stages. 



12. That consequently, though the Southern Drift preceded the 



Westleton Shingle, the two must at one time have proceeded 

 synchronously, though possibly at times on different levels. 



1 3. That the valley-system of the Wealden area had its origin after 



the Diestian or earty Pliocene epoch, — the initial direction of 

 the transverse valleys dating from Pre-Glacial times, and of the 

 longitudinal valleys from Glacial times. 



14. That the formation of the Thames Basin is the result, on the 



one hand, of the elevation of the Wealden anticlinal, and, on 

 the other, of the flexures of the Chalk and Oolitic strata in the 

 midland counties, and dates therefore from a period subsequent 

 to that of the Westleton Beds. 



15. That the genesis of the Thames dates in like manner from 

 late Pre-Glacial or early Pleistocene times, whilst its con- 

 nexion with its upper tributaries and the Isis took place during 

 the subsequent Glacial period. 



EXPLANATION OF PLATE VIII. 



This Map shows the position of the outliers of Westleton Shingle and of the 

 Plateau-gravels in the Thames Basin, with the lines of section given in PI. VII. 

 A line marks the southern limits of the Boulder-clay, but the other Glacial and 

 Post-Glacial drifts are not given. 



