132 COLE : ORIGIN AND FORMATION OF WOLD DALES. 
2. Then what has subaerial denudation done to them 
during the tens of thousands of years which have elapsed 
since the glacial period ? Of course, to some extent, they 
have participated in the general lowering of the surface by 
the chemical action of rain-water, which dissolves so many 
grains per annum of lime (see Appendix F, with tables) ; 
but, as to the mechanical action of rain and other subaerial 
agencies, there is nothing to show for it in all this long 
sequence of years but a little talus which has, here and 
there, been washed down and spread over the level surface 
below, and the little couloir down which it rolled. 
Now the valleys must have been formed, and probably 
have attained their present contour, before the beaches were 
deposited, which rest upon their sides. 
We gather then two or three important results : (1) That 
the effect of subaerial denudation in the erosion of the dales, 
since the glacial epoch, has been approximately nil ; (2) that 
the valleys must have existed before the last emergence, a 
fortiori before the last submergence, for the sea is confessedly 
a leveller, not an excavator ; and (3) that the present 
valleys were affected as much as the present tableland, and 
in all probability far more, by the great mantle of ice which, 
in the glacial epoch, pressed upon hill and dale with unknown 
but immense thickness, as it does upon Greenland now.* 
Hence we may safely conclude that the dales are the 
paths by which the then glaciers ploughed their way to the 
sea, or rather to the great central glacier which filled up the 
North Sea. The sinuous windings, the deep indentations, 
the beautifully regular, steep, and curved outlines, f the level 
gently sloping bottoms, added to the fact that the debris of 
the upper dales has been removed, and deposited at a lower 
level of several hundred feet, all point to this agency as a 
grand feature of their formation. 
* Jukes and Geikie, p. 703. f Ibid., p. 702. 
