224 A. C. RAMSAY ON THE PHYSICAL 



land, the plane surface of which near the Arans is about 1900 feet 

 above the level of the sea, or more than 1000 feet below the summits 

 of the neighbouring mountains. All intersected by unnumbered 

 valleys, to the ordinary observer it is merely a hilly country, while 

 an eye versed in physical geology at once recognizes that all the 

 diversities of feature are due to fluviatile erosions that have scooped 

 out the valleys. 



This brings me to the main object of this memoir, the origin and 

 geological date of the valley of the Dee. 



The country having been upheaved after the deposition of the 

 Carboniferous strata, and a large part of these strata having been 

 removed by denudation, the valley of the Dee did not then exist, or 

 existed only in a very rudimentary stage on the surface of a wide 

 slightly undulating tableland having a gentle slope towards the east. 

 It was then that first the Permian rocks were deposited, and after- 

 wards the New Red Sandstone and Marl ; and it may be recollected 

 that, at all events in my opinion, both sets of these formations were 

 deposited in inland salt lakes or seas. During these epochs, there- 

 fore, I hold that the old tableland lay high above the level of the 

 sea, probably even higher than it does now, and that it formed part 

 of a wide continental area. 



After the Trias came the Jurassic formations, deposited around 

 groups of islands in shallow seas, the effect of partial submergence 

 of an older land, and themselves, in the middle and north of England, 

 partly of fluviatile origin, the result of minor oscillations of level. 

 Then followed the long fluviatile conditions under which the Purbeck 

 and Wealden beds were deposited, during which epoch the greater 

 part of what is now Britain must have remained as part of a much 

 larger land. After this came the Cretaceous formations, the lower 

 half of which in the British area were certainly deposited near 

 shore ; while in later times, during the deposition of the Chalk, there 

 is no proof that the higher parts of Wales were submerged, but 

 rather the opposite. Later still come the Eocene deposits, some of 

 them of freshwater origin, and which in a large sense may be re- 

 garded as estuarine, even including the London Clay, which seems 

 to have been formed at the mouth of a great river such as the 

 Amazons or the Ganges. Our Miocene rocks are unmistakably of 

 terrestrial and freshwater origin ; and the different members of the 

 Crag were mere eastern shallow-sea or shore deposits. 



It thus appears that, since the beginning of the Permian epoch, 

 the higher ground of Wales has formed land well raised above the 

 level of the sea ; and even if there be some doubt about this with 

 respect to the time of the deposition of part of the Chalk (to which 

 doubt I do not attach much importance), that must have been but a 

 short episode when compared with the whole of the terrestrial 

 period. 



During that long lapse of geological ages, there was therefore 

 ample time for the action of all the ordinary processes of subaerial 

 denudation, the most powerful of which is the action of rain, rivers, 

 and glaciers. 



