Yol. 68.] POST-GLA.CIAL CHAJSTGrES IN THE LOWEE DEE VALLEY. 195 



pre-Glacial configuration is to be derived from this source. The' 

 lowest wells of which I have records are shown in fig. 3 (p. 193) : — 



Feet above O.D. 



Near the Trench (a mile and a half N. by W. of ends 



Ellesraere) at about 150 or less.'- 



Haugbton (half a mile N.E, of Ellesmere) . „ 210 or less, 



Gadlas „ 210 or less. 



Oolmere Wood (2^ miles S.S.E. of Elles- 

 mere) ,, 230 or less.1 



Petton (6 miles S.S.E. of Ellesmere) „ 180 or less.^ 



These tell us but little : for, although they represent depths up to 

 150 feet, yet the Drift might easily be twice that thickness in this 

 district. 



If we attack the question in a different way, and try to trace 

 the pre-Glacial watershed of the Dee Yalley, we are met with 

 difficulties which are again due to the covering of Drift. Certain 

 parts of the watershed, however, can be seen and may be summarized 

 thus : 



1. On the west the Welsh Hills form a definite barrier. 



2. On the south, round Knockin, West Felton, and E-uyton, the solid 

 rock lies at about 300 O.D. 



3. On the south-east the Grinshill E,iclge runs from Middle to Weston 

 and may, on the east, join up with the Prees outlier of Lias. 



4. On the east are the Peckforton Hills and their continuation south 

 to the east of Overton. 



Thus we cannot produce evidence that the Severn and Dee did 

 not join. There is, however, definite proof that the Severn did 

 not, in pre-Glacial times, flow through either the gorge at 

 Shrewsbury or that at Ironbridge. For at Dunn's Heath near 

 Leaton, north of Shrewsbury, the base of the Drift descends 50 feet 

 below the rock-lip of both these gorges. "^ We have confirmation 

 here of the view, advanced independently by Prof. C. Lapworth " 

 and Mr. Harmer/ that the Ironbridge Gorge is post-Glacial in 

 origin. 



The northerly trend of the pre-Glacial Severn drainage thus indi- 

 cated is a strong point in favour of the view that the two buried 

 valleys under discussion are really continuous, and further suggests 

 the possibilit}^ of the Severn having helped to excavate the deep 

 valley hidden below the Cheshire plains. At present I can offer no 

 convincing evidence in favour of or against this latter hypothesis. 



It will be noticed on the map (fig. 3, p. 193) that a course for 

 the pre-Glacial Dee has been suggested just east of Whittington, 



1 Fide Geological Survey Map, O. S. Sheets 73 N.W. & 73 S.W. 

 ■^ Charlotte Eyton, 'On the Pleistocene Deposits of North Shropshire' Geol. 

 Mag. Tol. vii (1870) p. 106. 



3 0. Lapworth, Proc. Geol. Assoc, vol. xv (1898) p. 425 ; 0. Lapworth & 

 W. W. Watts, in ' Geology in the Field ' Jubilee vol. Geol. Assoc. (1909-10) 

 pp. 768-69. 



4 F. W, Harmer, ' On the Origin of cei'tain Caiaon-like Yalleys associated 

 with Lake-like Areas of Depression ' Q. J. G. S. vol. Ixiii (1907) pp. 477-81. 



