1899] THE DEVELOPMENT OF RIVERS 289 



is called "Northern Drift" was deposited. The Upper (Shropshire) 

 Severn has done very much more. But perhaps there are two deposits 

 confused in the term " Northern Drift " — a high-level drift, and a 

 retransported low-level drift. 



The question why Triassic debris is found on the Moreton divide, 

 and not on the Chelt or any of the western divides, may be easily 

 answered. Eivers flowing from the west of May Hill, Malvern, etc., 

 country would come — at the level of the Chelt divide — off Palaeozoic 

 rocks straight on to Lias. 



But other queries in this connection will occur, to which answers 

 will be necessary. 



The date of an obsequent river like the Frome in the Stroud 

 valley can be approximately fixed by the gravels. In the valley just 

 below Stroud there are gravels with mammoth remains. And so the 

 obsequent valley had been deeply, and it would seem widely, excavated 

 before that date of Pleistocene geology. Since that date the river has 

 lowered its bed some 40 or 50 feet. 



In the Chelt valley, near my house, are several gravel pits. Up 

 the valley there is almost entirely Jurassic, mostly Oolitic material. 

 Coming down the valley there is found a greater and greater admixture 

 of a quartz sand. Beyond the valley there is wholly sand. Farther 

 west there are Triassic materials. 



The sand mixed with the Jurassic gravel is not local — not from 

 the Cotteswold Hills ; it is probably from the Trias rocks. How it 

 was brought up the Chelt valley may admit of more than one 

 explanation. 



There is much to be done with the gravels. After the Severn had, 

 as it is supposed, captured most of the western drainage, and had 

 started the Avon into the Midlands to see what it could filch, there 

 then remains a long period of history attached to the widening and 

 deepening of the Severn valley. 



REFERENCES 



1. •' Cheltenham as a Holiday Resort," Cheltenham, 1895. 



2. "The Cleeve Hill Plateau," Quart. Joum. Geol. Soc. 1897, vol. liii. p. 607. 



3. H. J. Osborne White, "On the Origin of the High Level Gravel," etc., Proc. Geol. 



Soc. 1897, vol. xv. pt. 4. 



4. W. M. Davis, "The Development of Certain English Rivers," Geogr. Joum. 1S95, 



vol. v. 



5. T. S. Ellis, "On some Features in the Formation of the Severn Valley as seen near 



Gloucester," Gloucester Phil. Soc. 1882. 



6. "Observations of a Cycle Tour," Proc. Cotteswold Club, 1898, vol. xii. pt. 3, p. 217. 



7. W. M. Davis, "La Seine, La Meuse, et La Moselle," Ann. Gcotjraphie, 1895, ~No. 19. 



8. J. Pkestwich, "On the Relation of the Westleton Beds," etc., Quart. Journ. Geol. Soc, 



1890, vol. xlvi. 

 3. J. W. GREGORY, "The Evolution of the Thames," Nat. Sci., London, 1894, vol. v. p. 97. 



Uhaklton Kings, 



Cheltenham. 



^0 NAT. SC. VOL. XIV. NO. 86. 



