COLE : ORIGIN AND FORMATION OF WOLD DALES. 137 
causes have probably contributed most to their present formation, 
whilst, for their origin, we must go back to the time when elevation 
first caused inequalities of surface by tension or compression. 
In the other diagram (D) the remarkable windings of the river 
Nidd illustrate well the propensity of running water to produce sinuous 
curves, but it does not appear that the river has had anything to do 
with excavating the Vale of York. It has simply confined itself to the 
work of excavating its own channel, and transporting a certain amount 
of sediment brought into it by the rainfall. Where there is no river or 
running water, as in the Wold dales, it is impossible to conceive either 
the excavation of valleys from this cause, or the removal by transporta- 
tion of the large amount of chalk rubble, which constitutes the bulk of 
the bottom gravels. 
Appendix D. 
In connection with this subject I would refer you to an interesting 
paper published by the Institution of Civil Engineers (No. 1,554, Vol. lv., 
session 1878-79, part 1), on the Chalk Water Supply of Yorkshire, bv 
my friend, Mr. J. E. Mortimer. Few men can speak with so much 
weight and authority on the geological and hydrographical features of 
the chalk area of the Wolds as Mr. Mortimer, who has devoted many 
years to a patient investigation of the facts under discussion. If I 
understand him aright, water, the produce of rainfall, is contained in 
the chalk, as in a sponge, in the interstices and pores of the mass, and 
finds its level by gradual infiltration, the line of saturation following to 
some extent the contour of the surface elevation, rather than that of 
surface depression. There is nothing whatever to show that the water 
drains into subterranean streams, which follow the windings of the 
dales, and are actively engaged in 'excavating them. This is a pure 
assumption, met at once by the fact that one of the principal dales, 
that, namely, from near Acklam Brow to Burdale has a bottom com- 
posed of [Kimmeridge] clay, on to the surface of which a subterranean 
stream from Wayrham to Thixendale (c/. Map A) ought to drain, 
supposing any such existed. But there is none. 
Appendix E. 
The thick mass of chalk and flint gravel which occupies the bottom 
of the dales, especially where they debouch on the plain of Holderness, 
and which is then spread fan-like over the level area, undoubtedly 
represents the matter mechanically denuded and transported from the 
valleys in the rear; but, in many cases, not transported far. The 
general character of the gravel partakes of that of the chalk in the 
immediate neighbourhood ; for example — the gravel one mile south of 
