ON THE PHYSICAL HISTORY OF THE DEE, WALES. 219 



25. On the Physical History of the Dee, Wales. By Professor A. 

 C. Ramsay, LL.D., F.R.S., V.P.G.S. (Read April 26, 1876.) 



[Plate XIV.] 



The surface of Bala Lake is 600 feet above the level of the sea, and 

 is bounded on the north-west and south-east by hills that near the 

 lake have elevations of about 1 200 aud 1300 feet, and therefore rise 

 to heights of 600 and 700 feet above its level, while at greater dis- 

 tances, but still not far off, they rise to heights of 1800 and 1900 

 feet. On the south-west there is a long gentle slope, which attains 

 a height of about 800 feet above the sea at the watershed close by 

 the road to Dolgelli, or 200 feet above the lake, beyond which the 

 river Wnion drains the country in a south-westerly direction into 

 the estuary of the Mawddach. 



The lake is about 130 feet in depth ; and at its north-eastern end 

 the waters of the Dee, escaping from this basin, first traverse an 

 alluvial tract nearly three miles in length, the detritus of which has 

 been carried from the adjoining hills by rivers, the largest of which 

 enters the Dee near Pont Treweryn, about half a mile below Bala. 

 Other good-sized streams form tributaries of the Dee below this 

 point, and have helped to distribute the materials of the alluvial 

 plain, beyond which, for a space of about a mile, the hills close in 

 upon the banks of the river between Glan-dwynant and Pont Llan- 

 derfel. Between this point and the neighbourhood of Corwen, the 

 river, for more than six miles, again wanders through broad allu- 

 vial flats, after which it flows in many curvatures, sometimes making 

 great loops, between the steep slopes of the vale of Llangollen, which 

 form the high and often flat-topped hills of Wenlock shale and slate, 

 that sometimes, not far from the river, slope up to 800 and 1200 

 feet above its banks. 



Leaving this part of the valley, the Dee, with an exceedingly tor- 

 tuous course, cuts through the marked escarpment of the Carboni- 

 ferous rocks of the Denbighshire coal-fields east of Llangollen, and, 

 passing through a less elevated tract of Permian strata, emerges on 

 the low undulating country of New Red sandstone south of Chester, 

 and finally, by a winding channel, enters the large tidal estuary 

 known as that of the Dee. 



Emerging from the Permian region at Erbistock, the country 

 through which the Dee flows to Chester may still be called a valley, 

 in so far that, miles to the west, there rises the long slope of Per- 

 mian and Carboniferous strata, while the eastern boundary is formed 

 of the escarpments of Keuper Sandstone of the Peckforton Hills 

 and Delamere Forest. Eliminating the minor modern effect on the 

 scenery produced by a shroud of glacial drift, with other geologists 

 I do not doubt that before the Glacial epoch the contours of this 

 wide valley were much the same as now, or, in other words, that, 

 like the valley of the Mersey and others in the west of England, 



Q.J.G.S. No. 127. r 



