226 
THE CRETACEOUS ROCKS OF BRITAIN, 
CHAPTER XTX. 
THE LOWER CHALK IN YORKSHIRE. 
General Description. 
The Lower Chalk of Yorkshire is, on the whole, similar to that 
of Lincolnshire. It emerges from beneath the Humber at North 
Ferriby, and the level of its outcrop rises rapidly as it is traced to 
the north-west, till near Leavening it is about 600 feet above the 
sea. Its strike then begins to change, the anticline of the Vale 
of Pickering giving it an east and west direction, so that it runs 
eastward, and at the same time falls in level till it passes beneath 
the sea at Speeton. 
The thickness of the Lower Chalk in Yorkshire varies considerably. 
Near South Cave it is about 72 feet; at the extreme north-west 
corner of the Wolds, near Leavening and Wharram, it is not more 
than 60 feet, and possibly less ; while at Speeton it attains a thick¬ 
ness of 123 feet. It is evident, therefore, that a rapid diminution 
of thickness takes place from east to west. 
Our knowledge of the Lower Chalk of Yorkshire, its limits, struc¬ 
ture, and fossil contents, is due almost entirely to Mr. W. Hill, 
who followed up his revision of the Lincolnshire Chalk by a thorough 
examination of the Yorkshire Lower Chalk, and the details given 
in the following pages are taken chiefly from his excellent paper, * 
supplemented by some information from a paper by Professor J. F. 
Blake, j and from the Geological Survey Memoirs by Mr. C. Fox- 
Strangways. 
Zone of Ammonites various. —Along the main escarpment 
this zone has the same general aspect as in Lincolnshire. At the base 
there is a bed of hard white limestone, often tinged with pink or 
yellow, and often passing down into the Red Selbornian limestone, 
just as in some parts of Southern England Chalk Marl passes down 
into Upper Greensand. 
* Quart. Journ. Geol. Soc., Vol. xliv. p. 320, 1888. 
f “ On the Chalk of Yorkshire,” Proe, Geol. Assoc., Yol. v. p. 232, 1878, 
