70 LAMPLUGH : NOTES ON THE WHITE CHALK OF YORKSHIRE. 
section for long stretches almost without alteration of level. Hence 
my measurements yield a further thickness of 105 feet only for the 
beds between South Sea and the base of the cliff on the southern 
side of High Stacks, where the first line of scattered nodules of 
grey flint is seen. (Appendix, p. 84.) 
In hammering along the section it has always seemed to mc that 
there is a very pronounced increase in the hardness of the chalk as 
the extremity of the headland is approached, and that besides the 
emergence of the more compact layers towards the base of the Flint- 
less Chalk there is an actual induration of the rock as a whole in this 
direction. This is a point worthy ol closer investigation, and if 
studied in connection with the numerous indications of compression 
and intimate rearrangement which the rock presents, might yield 
results of interest. The molecular movements necessary to the 
formation of the masses of flint in the underlying strata may be 
partly responsible for this induration, but a more probable cause is 
the proximity of the zone of contortion and faulting which is 
revealed in the cliff in Selwicks Bay, 300 yards northward of High 
Stacks. 
It is to be noted that up to this point there is a complete 
absence of flint nodules in the Chalk : and the qualified descriptions 
which have been applied to this portion of it, as containing " little 
or no flint," " almost destitute of flint," etc., are therefore rather 
misleading. If any silica be present it is invisibly disseminated 
throughout the mass of the rock,* or is incorporated in the fossil 
sponges, and is nowhere segregated into ''flints." 
From the above figures it appears necessary that we should 
assign to the Flintless Chalk of the vicinity of Flamborough Head a 
total thickness of not less than say, 650 feet. This doubles the 
highest previous calculation, namely that of Professor Blake, who 
estimated its depth at 320 feet. And as it is more than probable 
that beds higher than any of those of the Flamborough and Bridling- 
ton area exist beneath the mantle of drift which covers Holderness, 
* See " On the Flints of the Chalk of Yorkshire," by R. Mortimer. Proc. 
Geol. Assoc., vol. v. p. 349. 
