VALLEY AXD ITS RELATION TO THE WESTLETON BEDS, ETC. 177 



ranging S.W. and N.E. through parts of central England, and of 

 which the direction is coincident with the parallel ranges of the 

 Chalk and Oolitic escarpments in that area. The Westleton beds, 

 when raised, consequently dipped east and south-east on an incline 

 at right angles to these elevation folds. 



The result of this has been, that whereas on the Norfolk coast 

 the "Westleton Beds are close on the sea-level, they rise westward in 

 Berkshire to the height of from 400 to 500 feet, and northward in 

 Hertfordshire and Buckinghamshire to 500 and 600 feet. Thus a 

 drainage from the raised area was established to the south-east, but 

 diverted eastward as it approached the already raised Wealden area 

 with its northward drainage. 



The Thames necessarily resulted from these tributary lines of 

 drainage ; but the river must have been restricted at first to the 

 Tertiary and Chalk Basin, Avith the Kennet (passing round the 

 Tilehurst Hills) as the main stream and source of the river. The 

 Chalk- escarpment was not breached by the Isis until later. This 

 river before that time probably fiowed to the north-east, parallel 

 with and between the Chalk and Oolitic escarpments, and emptied 

 itself into the Wash on the east coast *. 



The old landmarks are, however, so obliterated by subsequent 

 Grlacial action and earth-movements that this requires confirmation. 

 Of the fact, however, that for some time after the rise of the Chalk- 

 escarpment, the pass of the Thames at Goring did not exist, and 

 that the first breach through the belt of Tertiary strata and Westleton 

 Shingle capping the Chalk-Downs Avas effected by a Clacial current 

 coming from tlie direction of Warwickshire and .Staffordshire, there 

 can, I think, be little doubt. It was not until the gorge was enlarged 

 by later glaciation, possibly aided by disturbances of the strata, 

 that the Isis was diverted into this new channel, and so formed :i 

 junction with the Lower Thames and Kennet. 



This may be illustrated l)y a diagram showing the two lines of 

 elevation with the resultant conditions of drainage (fig. 10). 



This is a branch of geology which opens some very large and 

 interesting problems. I have treated it briefly. Owing to the vast 

 erosion of tlie surface, the evidence respecting the older Drifts 

 is generally veiy fragmentary, and has often been entirely swept 

 away. Some speculation is therefore unavoidable, though it is 

 essential that the consequences that may result from hypothetical 

 assumptions should be in harmony with the results of observation. 

 In putting together my notes, many neAV views have suggested 

 themselves to me, and 1 should much like, as 1 have before 

 said, to have gone over the ground again, with the object of 

 confirming or, if necessary, correcting my early work ; l)ut tliat is 

 no longer possible, and I must leave the task to my younger 

 colleagues. 



* The width of the Wash belween J^ynn and Boston, and \\\e extent of the 

 Bedford level and adjacent marsh-lands, convey the idea precisely of the 

 estuary and alluvium of a large river, such as the Isis with its ti-ihutaries 

 would, in the case here suggested, have been. 



