522 Correspondence. 



across tlie Plain of York to the Humber gorge. Tbat is, the hard 

 Oolites and Chalk of the York wolds on the north and of the Lincoln 

 heights and Lincolnshire wolds on the south, have formed the gorge 

 of the Humber, which once flowed as high and higher than these 

 heights. In the meantime rain and the rivers have always excavated 

 deep flat valleys in the soft Triassic strata west of these heights and 

 have deposited patches of alluviums in them ever varying in height 

 with the ever varying level of the bed of the Humber gorge. Now 

 that the Humber gorge is cut down to the level of the sea, these 

 alluviums (like all alluviums next the sea or deltas) will constantly 

 rise from overflow and deposit, except where they are embanked. 



G. G. 



MARKS OF SEA-ACTION OJST THE CLIFFS, GORGES, AND VALLEYS 



OF WALES. 



To the Editor of the Geological Magazine. 



SiK, — Having not long since explored a considerable portion of 

 the country described by Mr. Mackintosh, in his interesting paper 

 on the " Cliffs and Valleys of Wales," chiefly with a view to study- 

 ing the physical geology of the district, I venture to ask space for 

 a few thoughts on "the great denudation puzzle." Admitting the 

 facts brought forward by my friend Mr. Maw, in his admirable 

 remarks on " Watersheds," and the general soundness of his argu- 

 ments, might we not still expect to find marks of marine-action in 

 the formation of beaches, the erosion of cliffs, etc., in precisely 

 those situations in which 1VL-. Mackintosh claims to have found them ? 

 And can such marks be considered, then, as any real evidence against 

 the subaerial theory of denudation ? These are the questions I pro- 

 pose very briefly to consider. 



Granting that the Eglwyseg cliffs, for, example, do bear marks of 

 having, at one time, been washed by the waves as those of Llan-, 

 dudno are now — if we mark the elevation of the supposed beach line 

 at their base, and trace out the line of such elevation on a contour 

 map of North and South Wales, shall we not get just such an intricate 

 outline of land and water, such a series of small islands, and land- 

 locked inlets, as Mr. Maw has shown to be found in the case where 

 a tract of land, with its recent configuration of hill and dale, is 

 Tcnown to have been suddenly submerged within historic times, but 

 which can not be found anywhere in the world where the sea washes 

 the coast of land long raised to any considerable height above its 

 level ? There was, beyond doubt, a period when the waters of the 

 Glacial sea covered the low lands of Cheshire, Flint, Denbigh, and 

 North Shropshire ; while such elevations as Wenlock Edge, the 

 Longmynd, Caradoc, and Wrekin-Cym-y-Brain, and Eglwyseg rocks 

 were above water, as well as the higher peaks. (Mr. Maw has 

 himself shown this in the case of Wenlock Edge, in his j)aper on the 

 " Severn Valley Drift," in the Quarterly Journal of the Geological 

 Society for May, 1864.) And we may reasonably look to find traces 

 here and there at the bases of those high lands of the action of the 



