5io Severn and Avon, Tewkesbury. 



my surmise is, that this same westerly and north- 

 westerly tilting of the Chalk of England formed a 

 gentle slope towards the mountains of Wales, as shown 

 in fig. 1 02, and the rivers of the period of the middle 

 and south of England at that time flowed westerly. 

 This first induced the Severn to take a southern course 

 between the hilly land of Wales and Herefordshire and 

 the long slope of Chalk then rising to the east. Aided 

 by the tributary streams of Herefordshire, it began to 

 cut a valley towards what afterwards became the 

 Bristol Channel, and established the beginning of the 

 escarpment of the Chalk, e, fig. 102, which has since 

 gradually receded, chiefly by atmospheric waste, so far 

 to the east. If this be so, then the origin of the valley 

 of the Severn between e and 1 is of immediate post- 

 Miocene date, and is one of the oldest in the lowlands 

 of England. 1 



The course of the Avon, which is a tributary of the 

 Severn, and joins it at Tewkesbury, is, I believe, of 

 later date than the latter river. It now rises at the 

 base of the escarpment of the Oolitic rocks east of 

 Rugby, and gradually established and increased the 

 length of its channel in the low grounds now formed of 

 Lower Lias and New Red Marl as that escarpment 

 retired eastward by virtue of that law of waste which 

 causes all inland escarpments to retire away from the 

 steep slope and in the direction of the dip of the 

 strata. 



If the general slope of the surface of the Chalk of 

 this part of England had been easterly instead of westerly 

 at the post-Miocene date alluded to, then the initial 

 course of the Severn would also have been easterly, like 



1 Many of the valleys of Wales must be very much older. 



