COLE : ORIGIN AND FORMATION OF WOLD DALES. 
135 
Appendix A. 
The question resolves itself into this — given two beds of chalk, one 
raised nearly 1,000 feet above the sea level, and exposed to atmospheric 
influences, the other lying below the sea level, though not under the 
sea, and completely covered up by a thick deposit of clay : which will 
wear away fastest ? There can be but one answer to this question, 
which it is needless to repeat. It must also be remembered that the 
disintegration of chalk by subaerial agency is carried on almost entirely 
by chemical action, not by mechanical. The quantity of chalk removed 
and carried off by springs in the form of hard water, i.e., water im- 
pregnated more or less with carbonate of lime (removal or transportation 
is a necessary element of denudation), is due to the presence of carbonic 
acid introduced by rain. Water can only absorb a certain proportion 
of carbonate of lime, then it ceases to act as a chemical agent. 
Hence, though the chalk is completely saturated with water in the 
lower beds (not geologically lower, but lower in altitude, as in Holder- 
ness), the chemically-denuding action of the rainfall is chiefly confined 
to the upper beds, i.e., to that portion of the chalk which is immediately 
exposed to the atmosphere. 
{Further remarks will be found under Appendix F.] 
Appendix B. 
It stands to reason that, in the process of elevation of any area of 
the earth's surface, waves and currents must exert a far greater influence 
on the slowly emerging portions than on those still buried in the depths 
of the sea. Even the highest points of the Wolds were once islands, 
exposed to waves, winds, and storms on the sides where now the smiling 
vales of York and Pickering lie basking at their feet ; and it is pre- 
cisely in these directions, west and north,* that the chalk ridges have 
been most attacked and worn into steep declivities, as at Acklam Brow 
and above Kirby Underdale, or else gradually thinned down, as at 
Grimston Brow, because then, as now, the fiercest gales came from those 
quarters. From these operations the chalk of Holderness would be 
protected by its then submarine position and mantle of clay. 
* Page— Geology, Advanced Text Bool; 2nd Edit., p. 293. 
