428 LOWER OOLITIC KOCKS OF ENGLAND : 
larly associated with grey and greenish clay, either of the 
constituents locally prevailing. In the area north of Ancholme 
Head, the thickness is from 15 to '20 feet. 
West of Waddingham Mr. Ussher obtained Modiola imbri- 
cata, Ostrea Sowerbyi, and Rhynchonella, from beds of bllie clay 
and loam under the Great Oolite Limestone. These are like the 
beds at Greet well. Beds of white and buff sand belonging to the 
Upper Estuarine Series occur in this neighbourhood and also to 
the east of Redbourne. The thickness of the Series is little more 
than 10 feet. The most northerly exposure occurs near Hibald- 
stow, where rubbly shale, dark grey and greenish clay and sand, 
were exposed beneath shaly Great Oolite Limestone ; but it is 
probable, as noted by Mr. Ussher, that the beds were penetrated 
in a deep boring at Brigg (see p. 430).* 
In 1875 Prof. Judd remarked that: " As we pnss northwards 
in the county of Lincoln, the Upper Estuarine Series, like the 
other members of the Great Oolite, becomes gradually reduced in 
thickness, and by the thinning out of the Upper Zone of the 
Great Oolite, the two argillaceous series, representing the Forest 
Marble and the Stonesfield Slate respectively, are brought 
together, thus the only vestige of the Great Oolite formation 
below the Cornbrash in North Lincolnshire is a thin series of 
clays of more or less estuarine character. "f 
Mr. Ussher states that : " West of Saxby, Owmby, and 
Normanby, the Great Oolite Limestone forms a rock of some 
economic importance, furnishing tolerably thick beds, suitable for 
building-purposes ; but the general tendency of the rock to split 
along lateral joints, or what might be called irregular incipient 
bedding-planes, is apparent even in parts of the best stone-beds. 
As we proceed northward the Great Oolite Limestone becomes 
more brashy, and there are beds in it so like Cornbrash, that a 
very detailed investigation was necessary to prove that the Corn- 
brash was absolutely nowhere in contact with the Great Oolite 
Limestone." Referring to the strata near Bishop's Norton, he 
remarks : (< We have here the typo so frequently exhibited by the 
Great Oolite from Snitterby northward, namely, the irregular asso- 
ciation of tolerably hard irregular shaly limestones with softer beds 
of decomposed fossiliferous limestone, or of broken shells in a 
loamy or clayey matrix. "J 
The Great Oolite Limestone in North Lincolnshire consists of 
shaly limestone, somewhat arenaceous in character and grey 
siliceous limestone, having the rubbly aspect of Cornbrash. Clayey 
beds are intercalated with the loAver strata north of Waddingham 
and Redbourne, furnishing evidence of a passage into the under- 
lying Upper Estuarine Beds. From the beds exposed in this 
district Mr. Ussher has obtained the following fossils : 
* Ussher, Geol. North Lincolnshire, pp. 81, 82. 
t Geol. Rutland, pp. 11, 186. 
J Ussher, Geol. Lincoln, pp. 65, 68. 
