44 



PHYSICAL GEOGRAPHY. 



CHAP. 



the sea was at higher levels than now, a theory established by 

 certain evidence, the results are very instructive. 



In Diagram XII. the sea is admitted to a height of 250 feet 

 above its actual level, in the valleys of the Thames, Severn, Nen, 

 and Ouse, the rivers being marked only in connection with the 

 Thames. At this level, the Thames Valley would be (must have 

 been) a vast estuary, with a sea-loch up the Kennet Vale ; straits 

 between the chalk hills of Chiltern and Lambourn; lochs right 

 and left up the Thame and the Ock ; straits near Abingdon ; and 

 again lochs right and left up the Ray and up the Thames; 

 narrower and far extended sea-channels up the Severn and the 

 eastern rivers. 



Under these conditions the Cotswold rivers may have delivered 

 abundant detritus, and formed gravel and sand beds of great extent 

 on the sides of the long loch of the Upper Thames, while from the 

 chalk hills considerable quantities of flints would be collected on 

 other parts of the shores. 



Diagram XIII. Land submerged 500 feet. 



Taking a different level, raising the sea 500 feet, we have the 

 aspect of land and water, as in Diagram XIII. a series of islands 

 branching out in a wide expanse of ocean ; the Cotswolds broken 

 up into many digitated masses ; the Thames basin confluent with 

 the Avon of Wilts and the Avon of Warwick ; no limit to the sea 

 on the eastward; still the straits of the chalk remain at Pang- 

 bourn; islets of the oolite near Oxford; and other straits appear, 



