bearing on theoretical Speculations. 26 1 



tified if any Fluvialist shall hereafter undertake the examina- 

 tion of the same phaenomena, and explain in detail, on his 

 own hypothesis, the exact manner in which the valleys of the 

 Thames and its tributaries can have been formed. 



Lest it should be imagined that the circumstances of this 

 river are in any manner peculiar, I will add a short examina- 

 tion of the various streams which traverse the portion of our 

 island occupied by the more horizontal strata, and in which 

 therefore the valleys are attributable to excavation rather than 

 dislocation. This district, as it is known, extends diagonally 

 across the island, from the south of Durham to the east of 

 Devon ; the more horizontal formations occupying all the 

 tract south-east of the diagonal line. Beginning our examina- 

 tion at the north extremity, the Derwent and its tributaries 

 first present themselves. 



1. First, as to the Rye, Did not a transverse valley open 

 across the oolitic chain of the Howardian hills, the waters of 

 Ryedale would form a lake discharging itself along the Vale of 

 Pickering at the base of the chalk escarpment, into Filey or 

 Scarborough bay. 



2. Had not the great transverse breach between the chalk 

 wolds of Lincolnshire and Yorkshire given vent to the outlet 

 of the Humber, all the flats near the junction of the Trent and 

 Derwent would have formed an immense lake, whose waters 

 would have been so dammed up as to have flooded all the 

 lower portions of the Ouse and Swale, and discharged them- 

 selves finally by the mouth of the Tees; as the escarpments 

 of the chalk wolds, and afterwards of the eastern moorlands, 

 would have presented an insuperable barrier, preventing any 

 other egress to the sea basin excepting Teesdale, previously to 

 their fracture by transverse valleys. Now in order to get over 

 this difficulty, the Fluvialist must, I conceive, argue that at the 

 time when his streams commenced their operations, the said 

 escarpments presented no barriers at all, all the valleys on the 

 west of them having been at that period filled up (by materials 

 since removed) to such a level as to overtop the chalk and 

 oolitic ranges ; since by such a configuration of surface alone 

 could the streams have been brought to act on these ranges so as 

 to cut transversely through them. Let the Fluvialist, however, 

 so reconstruct the district in question : I next ask what it will 

 require to reduce it from this " its form ten million years 

 ago " to its actual features ? Why simply the excavation of 

 the entire vales of Lincoln and York (a district about 100 

 miles long and more than 15 broad) to a depth of 700 feet 

 beneath its supposed original level. I will ask but one other 

 question, How long would atmospherical drainage take to effect 



this ? 



