4 



80 PROF. T m'kenny hughes on the 



This drift belongs to a period of submergence of which there is 

 other evidence all round the coast of Wales. Hence it is clear that 

 we must divide it into two stages, the deposits of the submergence 

 and those of the emergence. There must have been the waste along 

 the shore of the encroaching sea as the land subsided, and ^the further 

 down the valleys sunk the safer from further denudation was the 

 debris swept into the deeper parts. There must have been shingly 

 shores and cliffs of boulder- clay of the Arenig Drift, along which 

 landslips took place, and the clay, not always broken up, and the 

 included stones, not always rolled, settled down into the fjords. 

 Round the shore there would be a shingly beach. 



Then there was the period of emergence, when the land rose to 

 where we have it now. This was, of course, a time of greater waste 

 and destruction, when the soft, newly-formed beds were lifted up to 

 the level of the wind-waves, or, if they survived the lash of the 

 waves, were raised out of the sea to be acted upon by the summer 

 sun and winter's frost — by the torrents of rain and the mountain- 

 streams. 



So we must expect to find along the margin of the valley more 

 sand and gravel, and towards the centre more clay. 



Now, to examine the sections in the drifts of these stages, 

 I will take them in an order convenient for my purpose of corre- 

 lation, first giving the most typical and clearly made out, and then 

 following them, as suggested by the particular points of variation 

 which I am endeavouring to explain. 



The river Elwy, when it has once turned north after breaking out 

 of the gorge under the Cefn rocks, generally clings rather to the 

 eastern side of the valley till it joins the Clwyd at E-hydyddaudwr, 

 above Bhuddlan. 



Down as far as Pontyralltgoch it cuts into stained Carboniferous 

 rocks capped by drift ; but soon the solid rock drops out of sight, 

 and the river washes the base of a slippery slope of clay and sand, as 

 seen where it cuts into the steep bank south of Brynelwy. 



The greater part of the drift seen in this section must be referred 

 to the St. Asaph Drift. The dark-blue boulder-clay sometimes ex- 

 posed at the base near the north end may be, as we have said above 

 (p. 76), the old Arenig Drift. A mass of gravel and sand at the 

 top, which may be the gravel of the shore during emergence, is 

 brought against the red clay by an ancient settlement, the exact 

 amount and direction of which is obscured by subsequent slippings 

 of the face of the cliff ; but they both belong to the same set of 

 deposits, and contain the same remains. 



In the wood, less than 100 yards to the south, more clay is seen, 

 but the lower part of the section there is obscured by talus and 

 overgrown. 



The upper sand and gravel is generally grey ; the clay is red. 

 Lower down the valley, about J mile south of the Palace of St. Asaph, 

 a similar dark-red clay with boulders rests upon sharp red sand, as if 

 derived largely from New Red Sandstone. North of the city, just 

 below the Mount, another section through the St. Asaph drift is 



