MIDDLE CHALK—'YORKSHIRE. 
485 
CHAPTER XLI. 
THE MIDDLE CHALK IN YORKSHIRE. 
fan General Description. ^ 
It might have been expected that the chalk of South Yorkshire 
would have been merely a continuation of that of Lincolnshire, but 
with respect to the Middle Chalk this is not the case, for diff erences 
present themselves as soon as we have crossed the Humber, not 
only in the lower zone of Rhynchonella Cuvieri but also in that of 
Terebratulina. 
The lower beds of the Rhynch. Cuvieri zone are an almost exact 
counterpart of the beds found at the same horizon in Lincolnshire, 
consisting of rough, yellowish, shelly chalk in beds of no great thick¬ 
ness for 13 or 14 feet. This, however, is succeeded by white chalk 
in thicker beds, sometimes without flints and sometimes with flints, 
scattered or in layers, but this white chalk is not like that which 
succeeds in Lincolnshire, being rougher and containing Inoceramus 
mytiloides. Of this chalk there is 26 feet at Hessle, and apparently 
about 50 near South Cave.* 
The Terebratulina zone also becomes somewhat thicker, though 
by how much it is thicker in South Yorkshire we do not yet 
know. It also develops near the base one or two beds of very 
hard compact chalk or chalky limestone, which bear a certain re¬ 
semblance to the Chalk Rock of more southern counties, but do not 
contain nodules of any kind. In other respects the chalk of this 
zone resembles that of Lincolnshire, containing similar grey flints, 
with occasionally a thin seam of continuous flint and frequent 
layers of grey marl. It is, however, rather more fossiliferous, both 
Ter. gracilis var. lata and Calerites subrotund vs occurring as well 
as the common Inocerami—i.e ., I. Brongniarti and I. Cuvieri. 
Mr. Hill’s recent observations, which he allows me to in¬ 
corporate in this chapter, show that the change from the 
Terebratulina zone (Middle Chalk) to the Hoi. planus zone (base of 
Upper* Chalk) is gradual, and similar to that in Lincolnshire. 
They also throw light on a point which has given rise to some 
difference of opinion, and that is the position of the beds containing 
Inoceramus mytiloides. Professor Barrois correctly recorded this 
fossil under the name of Inoc. labiatus from the lowest part of the 
R. Cuvieri zone, and Inoc. Brongniarti from the overlying chalk 
with flints. The Rev. J. E. Blake maintained that the shell in the 
This statement is based on information obtained recently by Mr. W. 
Kill, see p. 480. 
4219. [ 2 
