380 
CHAPTER XIII. 
GREAT OOLITE SERIES. 
2. NORTHAMPTONSHIRE TO LINCOLNSHIRE. 

GENERAL ACCOUNT OF THE STRATA. 
IN the area extending from Northamptonshire and Buckingham- 
shire, through Bedfordshire into Lincolnshire, the strata between 
the Inferior Oolite Series and the Cornbrash are divided as 
follows : 
Great Oolite Clay (Blisworth Clay). 
Great Oolite Limestone. 
Upper Estuarine Series, 
In total thickness they vary from about 30 to a little over 100 
feet. 
A general description of each division will first be given ; and 
the local details of the strata of the three divisions, may then most 
conveniently be described together. It may here be observed 
that for our particular knowledge of the strata in this area, we are 
indebted to Prof. Judcl, whose observations were made during 
the course of the Geological Survey ; to Samuel Sharp ; and 
to the officers of the Survey who subsequently carried on the 
work in Lincolnshire. 
It will be obvious that in this conformable and variable series, 
it is not possible to correlate exactly each portion of the strata 
with the divisions found in the area to the west and south-west. 
Even the above divisions are not likely to correspond more than 
approximately in the planes of division locally taken to separate 
them. 
UPPER ESTUARINE SERIES. 
The occurrence of fluvio-marine beds yielding plant-remains, 
Cyrena, &c., above the limestones of Ketton and Casterton 
(Lincolnshire Limestone), was pointed out by John Morris, in 
1853, although the age of the underlying limestones was not at that 
time rightly interpreted, and the strata in question were regarded 
as the equivalents of the Forest Marble.* 
To these strata Prof. Judd, in 1867, applied the name Upper 
Estuarine Series, and he then stated that they " appear to 
represent the Stonesfield Slate or Lower Zone of the Great 
Oolite of the South of England."t 
* Moms, Geol. Mag., 1869, p. 102. 
t Geol. Rutland, pp. 90, 189. 
