Mackintosh— On tie Cliffs and Valleys of Wales. 393 



our present sea-coasts. To the right there is a basin with three 

 outlets. The "Wye enters on the right hand behind G-anallt Hill, 

 and escapes by the valley in the foreground. In the background 

 there is a basin with lofty cliffs, one side of which is skirted by the 

 Wye, and into this basin a small brook enters from the west by a 

 series of cascades, or rather water-slides (the latter not represented 

 in the sketch). The sides of the basin look very unlike any clifis 

 the river is now forming, and no trace of river-drift can be found at 

 an elevation of more than a few yards above the river. A very 

 powerful current must here have entered a previous hollow, or 

 series of hollows, and by a gyratory movement scooped out the 

 basin. 



On arriving at Marteg Bridge the Wye is joined by the Marteg 

 Eiver. As we proceed along the banks of the latter by railway, we 

 see the most extraordinary complication" of gorges, some with 

 streams, some dry, but generally speaking the size of the stream is 

 not proportioned to the size of the gorge. During the journey to 

 Llanidloes many short Y-shaped gorges on the sides of hills or 

 table-lands, may be seen, some with, and some without streams. 



Action of the Sea at Aberystimjth. — A whole article might be 

 written on the gorges, cwms, and precipices to the south of Llan- 

 brynmair station, but I must hasten to the sea-coast. At Aber- 

 ystwyth the subaerial geologist will find himself in comfortable 

 quarters. Here the sea is forming a plane of denudation, and cutting 

 with equal facility along the sides, and across the ends of ridges 

 and valleys, without producing indendations beyond a small cwm. 

 Were the floor of the sea to be elevated, we should here have a land 

 plain bounded on the eastern side by an escarpment, with rivers 

 debouching on the plain where they now enter the sea. But are 

 we to conclude from this that the sea produces nothing but planes 

 of denudation, and that it can only originate land surfaces in the 

 form of plains with bounding escarpments ? It is a remarkable fact 

 that in channels, and on comparatively protected coasts, the sea 

 generally forms approximately straight lines of cliff; but what do 

 we find on the western shores of Ireland,^ Scotland, and Norway, 

 where the land is dh-ectly confronted by the sea, and exposed to 

 the full fury of storms, and the undeflected force of currents ? K 

 some of the sea-lochs and fiords can be shown to be submerged land- 

 valleys, this argument will not apply to all deeply indented sea- 

 coasts, for the following reasons : — At any given time tlie greater part 

 of the earth's surface must be covered by the sea ; during the gradual or 

 intermittent submergence and re-emergence of the land, every part of it in 

 succession must figure as a sea-coast ; the average time- required for a 

 submergence and re-emergence must be sufficient to allow the sea to efface 



1 "Why is not the sea cutting across ridges and valleys on the west coast of Ireland ? 

 Because in Ireland it is now forming ridges and valleys as it ancientli/ did in Wales. 

 On any given coast the sea must be either destroy big or producing inequalities ._ 



- Any given area of the earth's surface must, during a given lapse of time, he 

 longer below than above the sea-level, otherwise the proportions of land and sea could 

 not be maintained. 



