GREAT OOLITE SERIES : THRAPSTON. 407 
Here there is evidence of a passage between the Great Oolite 
Limestone, and overlying Clay ; and it is unlikely that the same 
plane of division would be taken in different localities. 
Prof. Judd states that about Brigstock and Stanion, both the 
limestones and oyster-beds of the Great Oolite are exposed at 
many points. Westward, about Great and Little Oakley and at 
Pipwell, they are also seen, but do not furnish any very good 
sections. The best is that afforded by the Great Oakley brick- 
yard, where we have 6 feet of Great Oolite Limestone, consisting 
of alternate courses, each about 1 foot thick, of Forest Marble- 
like stone, and marly oyster bands, containing Ostrea subrugulosa 
and O. Sowerbyi. Under the rock there occur black, carbonaceous 
clays, and, still lower, light, variegated clays ; both belonging to 
the Upper Estuarine Series. 
He also observes, that by the roadside, half a mile east of 
Sudborough Church, a pit in the Great Oolite Limestone exhibits 
a thick bed of rock, somewhat oolitic (as in the pit at Geddington 
Chase), and covered by an oyster-bed, with the usual characters, 
about 1 foot thick. Above the oyster-bed there is a considerable 
thickness of variegated clays with stony bauds, representing the 
Great Oolite Clay. 
Some of the beds of limestone in this neighbourhood are flaggy, 
and shelly, like the Forest Marble of the south of England, 
having diffused through their masses a few oolitic grains.* 
Northampton to Thrapston, Oundle, and King's Clijfe. 
Reference has been made to the attenuation and even absence 
of the Northampton Beds (as well as the Lincolnshire Limestone), 
in the country between Northampton and Newport Pagnell. 
There is thus evidence of much unconformity between the members 
of the Great Oolite Series and underlying strata. Over much of 
this area the Upper Estuarine Beds have not at present been 
mapped, although they have been traced here and there along the 
outcrop, on the southern side of the Nene valley, at Castle Ashby 
and Wollaston. The beds are not very thick, and there is much 
Drift, so that the apparently impersistent nature of the outcrop 
is due probably to the fact that no evidence of these Upper 
Estuarine Beds has been obtained, in places, as at Bozeat. 
Wherever sections have been opened, the beds have been seen to 
occur at the base of the Great Oolite Limestone. 
The unconformity betAveen the Upper Estuarine Series and 
beds below, is of a more marked character in some areas than in 
others, as near Draughton ; while at Stanwick and Irthlingborough, 
the Northampton Beds are so reduced in thickness, as not to have 
been marked on the Geological Survey Map, and the Upper 
Estuarine Beds are shown to rest directly on Upper Lias. 
The following series of beds was noted by me in a quarry and 
cutting on the Midland Railway south of Thrapstoaf (Fig. 1 13) : 
* Judd, Geol. Rutland, pp. 212, 213. 
t See also Sharp, (who records focsils from this locality), Quart. Journ. Geol. 
Soc., vol. xxix. p. 281. 
