COLE : ON THE RED CHALK. 
31 
south. And the Chalk Marl, Ujoper Greensand, and Gault, 
amounting in the south to some 400 ft. altogether, are but 
slightly represented in the north by a band of red or grey 
chalk, seldom exceeding 40 ft., and a small patch of Upper 
Greensand in the neighbourhood of "Welton. 
It is to this red or grey chalk that your attention is 
directed. It lies at the base of the white chalk, and is 
absolutely flintless. As a rule it follows the contour of the 
Chalk "Wolds on their northern and western escarpments, 
and is so delineated by Professor Phillips. From the accu- 
mulation of surface soil, it can only be seen in situ in a few 
places ; but its locality may be infallibly determined by the 
numerous springs which issue from its junction with the 
Speeton or Kimmeridge clay beneath. Being for the most 
part a comparatively thin deposit, its chief importance lies 
in the fact that by it we are enabled to trace the elevation 
of the base of the true chalk, above the vale of Pickering 
on the north, and the vale of York on the west, and con- 
sequently the thickness of the chalk at points of its highest 
elevation. 
Many persons glancing at a physical map, or obtaining 
a view of the precipitous sides of the wolds from the railway 
from York to Scarbro', might suppose that the hills were 
composed of chalk to their base. 
But this is not so ; it is only at the two extremities, at 
Speeton on the one hand, and near the Humber on the other, 
that the red chalk comes down to the level of the plain. 
At the north-west corner of the wolds, from above North 
Grimston, round by Acklam, to Kirby Underdale and 
Bishop Witton, the red chalk lies at an average elevation 
of about 450 ft. above the sea level ; so that the outer hills 
are only capped with chalk, the base being composed of 
Kimmeridge clay and Corallian rocks. 
It is clear, in fact, that the chalk is thinnest at its 
