152 PROCEEDINGS OF THE GEOLOGICAL SOCIETY, [Feb. 7, 



or nearly flat-lying Secondary formations that now form great part 

 of France and England (then united), were so far affected by this 

 renewed upheaval of the Alps and Jura, that they were all tilted at 

 low angles to the north-west. That circumstance gave the initial 

 north-westerly direction to the flow of so many of the existing 

 rivers of France, and led them to excavate the valleys in which 

 they run, including the upper tributaries of the Loire and Seine, 

 the Seine itself, the Marne, the Oise, and many more of smaller 

 size ; and 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, and the rivers of the middle and south of Eng- 

 land 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 rising to the east ; and, 

 aided by the tributary streams of Herefordshire, it cut a channel 

 towards what afterwards became the Bristol Channel, and estab- 

 lished the beginning of the escarpment of the chalk (e, fig. 4, p. 154), 

 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 

 is of immediate post-Miocene date, and it is one of the oldest in 

 England *. 



The Avon, which is a tributary of the Severn, and joins it at 

 Tewkesbury, is, at all events, partly of later date. It rises at the 

 base of the escarpment of the Oolitic rocks east of Rugby, and gra- 

 dually established its channel in the low grounds formed of Lower 

 Lias and ISlew Red Marl, as that escarpment retired eastward by 

 virtue of that law of waste, that all inland escarpments retire op- 

 posite to the steep slope, and in the direction of the slope of the 

 strata. 



If the general slope of the surface of the chalk 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, Hke that 

 of the Thames and the rivers that flow into the Wash and the 

 Humber. 



This at once leads to the question, Why is it that the Thames 

 and other rivers that flow through the Oolites and Chalk run east- 

 ward ? The answer seems to me to be, that after the original vaUey 

 of the Severn was cut out by its river a new disturbance of the 

 whole country took place, by which the Cretaceous and other strata 

 were tilted eastward, and not suddenly, but by degrees, an initial 

 slope was given to the Chalk and Eocene strata, east of the com- 

 paratively newly formed escarpment of the Chalk indicated by the 

 dark line in fig. 4, marked e. The Chalk escarpment, in its beginning, 

 is thus of older date than the Oolitic escarpment, though it would 

 be hard to find this out except on the hypothesis I have stated. 

 The Thames, then, in its beginning, from end to end, flowed easterly 

 over Chalk and Eocene strata, and the river was larger then than 

 now. But by processes of waste identical with those that formed 

 the escarpment of the Wealden, the Chalk escarpment gradually 



* Many of the valleys of Wales may be much older. 



