554 Fisher — Denudations of Norfolk, 



and on land the streams flow more swiftly, and earthy matter is more readily 

 movable, when the fall is increased. 



If we knew the scouring force of marine currents in any locality, we could cal- 

 culate exactly the rapidity with which an area might be elevated, so as to keep it 

 just submerged. Upon this eastern coast we know the scour to be very considerable. 

 The instance given by Mr. Gunn is much to the purpose.^ Mr. Cubitt, of Bacton, 

 informed him that vessels can now sail at high water, where, no more than thirty- 

 five years ago, land was cultivated, and I have already referred to an instance at 

 Walton-on-the-Naze, where the depth of water is constantly increasing beneath the 

 jetty. In fact, it is self-evident that the sea over any given spot off this coast is 

 gradually becoming deeper — in other words, marine denudation is progressing. 

 From such considerations it would appear that the true measure of denudation is 

 the rate of the elevation of the land (or depression of the sea) up to a certain 

 value of that rate ; so that, under favourable circumstances, submarine denudation 

 may go on much more rapidly than we are apt to suppose. 



As soon, however, as the rate of elevation begins to exceed the rate of denuda- 

 tion, dry land will make its appearance. And in every place where dry land exists 

 this must have happened ; and it appears to me to be an argument for much more 

 rapid movements of the surface than we usually suspect. 



Let us now trace what would seem to be the consequence of the rate of upheaval 

 exceeding that of marine denudation among such strata as we have hereabouts. 

 The surface, as has been shown, I believe, by Professor Ramsay, would emerge as 

 an approximate plane of considerable extent. Inequalities would exist upon it, so 

 that the sea would run up into inlets around the coast, and in the intervening parts 

 the waves would commence the formation of cliffs. Now, as the elevation con- 

 tinued, what would become of those cliffs ? Would they be raised high and dry, 

 and form escarpments inland? I think not. As the land rose, the beach would be 

 constantly swept away, and the cliffs would continue to be sea cliffs, being still cut 

 back, but more slowly than if the land were stationary. Around the shores of the 

 estuaries, however, where the force of the waves was less, the beach might possibly 

 be raised high and dry by a rate of elevation too small to produce the same effect 

 on the open coast. It follows, then, that the present sea cliffs will in the main be 

 the true representatives of the original cliffs, which began to be formed when the 

 land first emerged from the ocean. They will, doubtless, by waste have been cut 

 back further inland, but they will be the true successors of the original cliffs. 



This, then, is another argument against inland escarpments among soft strata 

 being old sea cliffs, in addition to those which have been frequently adduced and 

 so well collected and commented on by Mr. Whitaker.^ 



I think it by no means certain, nevertheless, that submarine erosion by currents, 

 (not by waves,) may not have acted more readily along the outcrop of soft beds, 

 and thus commenced the valley systems which have been intensified, and brought 

 into their present contour, by subsequent subaerial action (using that term as the 

 opposite to submarine). I suppose that the gravels, which may be conceived to 

 have resulted from such action, are what Mr. Searles Wood calls in his writings 

 *' denudation gravels." But the general absence of marine extivice of every kind is 

 a difficulty in this view of their formation. 



It will be understood, then, that I should attribute the removal of the vast 

 amount of rock which has disappeared from this area, to the action of the sea. 

 But not so the present contour of the surface. I believe few doubt that that has 

 been produced subaerially by some agency disintegrating the surface and carrying 

 it downwards into the sea, thus scooping out the valleys and leaving the hills out- 

 standing. 



I need not recapitulate on this occasion the arguments which have been adduced 

 by many to show that this work has been effected by rain and rivers, but I may be 

 permitted, and indeed I conclude that, by the present task having been assigned to 

 me by the local committee, I am expected to give a short account of my own views 

 upon the subject. 



In such a country as this, where many of the strata consist of mixtures 

 of clay with large flints, and boulders of igneous and other hard rocks, I can- 

 not conceive how rain can have cleared them away. '^ The difficulty is the same 



1 Geology of Norfolk, p. 26, 2 Geol. Mac, vol. IV., pp. 447, 483. 



' See Mr. Mackintosh's letter Geol. Mag,, vol. IV. p. 571. 



