GREAT OOLITE : UPFEU ESTUARINE SERIES. 
The strata consist of blue, purple, white, and variegated clays 
of a more or less sandy character, with pyrites, selenite, lignite 
and occasional and irregular layers of limestone. In many of their 
characters, therefore, they resemble the Lower Kstuarine Series, 
and when the two series come together it is difficult to distinguish 
ihem. 
Prof. Judd remarks that " Interstratified with the clays are 
bands of sandy stone, with vertical plant-markings and layers of 
shells, sometimes marine, as Phdladomya, JModiola, Ostrca, Neara, 
c., at other times fresh-water, as Cyrena, Unto, \_Paludina], &c. 
Beds full of small calcai'eous concretions and bands of " beef" or 
fibrous carbonate of lime, also frequently occur, and the sections 
sometimes closely resemble those of the Purbeck series. In its 
lower part this series consists usually, but not always, of white 
clays passing into sands." At the base of these clays there is 
usually found a thin band of nodular ironstone, seldom much 
more than one foot in thickness ; this " ironstone junction-band " 
is generally conspicuous, and marks the limit between the Great 
and Inferior Oolite Series in the district. " There is very decided 
evidence of a break, accompanied by slight unconformity, between 
these two series in the Midland area. All the characters presented 
by the beds of the Upper Estuarine Series point to the conclusion 
that they were accumulated under an alternation of marine and 
fresh-water conditions, such as takes place in the estuaries of 
rivers." (See Figs. 48, 51, and 53, pp. 169, 188, and 191.) 
The break to which Prof. Judd refers, is undoubtedly a well- 
marked one ; but the unconformity is sometimes intensified by local 
dissolution of underlying calcareous beds?. The ferruginous nodules, 
though generally found at the base, are not confined to that 
position; they are probably of much later date than the 
accumulations in which they occur. 
The beds vary from 15 to a little over 30 feet in thickness. 
Near Northampton the thickness is 15 feet ; near Bedford, 27 feet ; 
at Aunby, near Essendine, 33 feet ; at Heighington, south-east of 
Lincoln, it is 35 feet; and further north the beds diminish in 
thickness. 
Prof. Judd remarks that, lying, as they do, upon a great mass 
of limestones (the Lincolnshire Oolite), the sandy clays of the 
Upper Estuarine Series are often found in "pipes," in consequence 
of the removal of the calcareous rock by subterranean waters, 
usually along lines of jointing. " Thus, patches of these strata are 
sometimes seen at considerable distances from their proper lines 
of outcrop ; but such " outliers," are of course, on too small a 
scale to be represented upon the map." This mode of occurrence 
is similar to that noticed in the f< Rift Bed " of the area near 
Chipping Norton. (See pp. 149, 325.) In that area the basement 
beds of the Great Oolite (Stonesfield Series), that are intimately 
linked with the Fuller's Earth, comprise marls and marly lime- 
stones, and yield, among other fossils, Modiola imbricata, Ostrea 
acuminata, O. subrugulosa, and Rhynchonclla concinna. 
