180 LOWKK OOLITIC ROCKS OF ENGLAND : 
Blis worth to Thrapston, Stamford, and Market Overton, beds of 
ironstone of variable character and thickness occur ; but in many 
cases the ore is too thin or too poor to work, while the beds in 
some places are represented only by sands or by ferruginous and 
calcareous sandstone. 
In the case of the Middle Lias ironstone, the ore, in Leicester- 
shire and other parts of the midland area, is not worked beneath a 
covering of Upper Lias clay ; but the Northampton ironstone is 
obtained often beneath thick coverings of Lower and Upper 
Estuarine Beds and Great Oolite, for in these cases, through the 
overlying beds being largely of a porous nature, the rock has been 
weathered to a considerable distance underground. The fact is 
that the brown iron-ore can be worked more profitably than the 
unweathered rock (carbonate of iron). 
Ironstone has been worked also in the outliers of Neville Holt 
and Uppingham, Ridlington and Preston, between Gretton and 
Bulwick, west of Oundle, at Southwick, &c. Traces of ironstone 
are also met with in the outliers of Whadborough, Robin-a-Tiptoes, 
and Barrow Hill. Near Normanton the ironstone is 8 feet thick, 
but at Ufford, south-east of Stamford, it is reduced to 1 foot. 
According to (Sharp's estimates, the ferruginous rock and asso- 
ciated sandstones must be nearly 50 feet thick in places, but the 
sections vary much in detail, and the thickness of the unprofitable 
green beds at the base, is also subject to yariation in different 
localities. The beds containing ironstone do not attain a thick- 
ness of more than 30 feet, and these as a rule do not yield more 
than about 10 or 32 feet of profitable ore. These ironstone-beds 
pass laterally to some extent into the "Variable beds" of Sharp, 
and these again into the White Sands, &c. of the Lower Estuarine 
Series. He noted the following local subdivisions *: 
FT. 
White Sands - - - . - . - 12 
Variable Beds, with '' Slate " at the base - - 34 
Ironstone - - - - - . -35 
These estimates of thickness are no doubt excessive if we add 
together the maximum thickness of each division. 
On Dane's Hill, near Northampton, the beds exposed were as 
follows : 
Northampton 
Beds. 
FT. IN. 
Rubble with bright red and pink 
staining in places - - 5 to 6 
White sand - -~] 
Bubbly iron-sandstone with " boxes "j 
of iron ore : the beds becoming )-12 
thicker deeper down - - - I 
Yellow ochreous iron- ore - -J 
The following section was noted at one of the Duston iron- 
stone-pits : 
* See Sharp, Quart. Journ. Geol. Soc., vol. xxvi. pp. 358, 380 ; vol. xxix. p. 228. 
