424 LOWER OOLITIC ROCKS OF ENGLAND : 
some of which are evidently Yery closely linked with the Upper 
Estuarine Series. 
Thus in a section in Griinsthorpe Park, noted by W. H. Holloway, some 
of these oyster-beds have been included in the Upper Estuarine Series, but 
the section was much obscured by talus, so that it is not clear that the 
classification there adopted is correct ; and it may be best to group with 
the Great Oolite Limestone, the beds of shelly limestone (6 to 10 feet thick) 
and the overlying marly oyster-beds, that there rest on the green and 
purplish clays of the Upper Estuarine Series.* Well-sections at Horbling, 
Billingborough, Dmisby, and Pinchbeck North Fen, indicate that the 
Upper Estuarine Series varies in thickness from 26 to 35 feet.f 
In the cutting near Eauceby station, Mr. ~W. H. Dalton noted a thick- 
ness of over 18 feet of shelly marls, and green, grey and purple clays, with 
layers of white and yellow sand at the base ; and from these beds Ostvea 
was obtained. A well at Leasingham, N.W. of Sleaford indicates 66 feet 
of dicey clay beneath the Great Oolite ; but this unusual thickness for the 
Upper Estuarine .Series requires confirmation. J 
The Upper Estuarine Beds have been well shown in the 
Haydor and Wilsford quarries, above the Ancaster stone 
(Lincolnshire Limestone). There grey shale and ferruginous 
layers occur at the base, and higher up we find purple and 
greenish shales and clays with thin bands of marly limestone. 
Above the Upper Estuarine Clays near the Windmill, at 
Ancaster, there are bands of grey marly, shelly, and sandy lime- 
stone, and flaggy calcareous sandstone, with Ostrea and Modiola, 
belonging to the base of the Great Oolite Limestone. 
Quarries in the Great Oolite Limestone were noted by 
"VV. H. Holloway near Ingoldsby, Walcot, and Pickworth. There 
we find 3 or 4 feet of marls, and shelly bands crowded with 
Ostrea Soicerbyi and 0. subrugulosa, and with occasionally a 
band of dark blue and greenish clay, overlying 3 or 4 feet of hard 
marly and shelly limestone with oolitic grains ; the stone is dug 
for road-metal. Near Sleaford the Great Oolite Limestone forms 
no conspicuous feature in the land. (See Fig. 117.) 
Well-sections at Horbling, Billingborough, Dum;by, Pinchbeck North 
Fen and Bourn, indicate the thickness of the Great Oolite Limestone to 
vary from 12 to 33 feet. At Swarby, S.W. of Sleaford, it is 24 feet, at 
Osbournby 14 feet, and at Leasingham to the N.W. of Sleaford from 
21to33feet. 
At Great Humby, informa.tion (derived from a well-section) shows 
that the Great Oolite Clay attains a thickness of 29 feet : it consists of 
blue and grey clays with thin rock-beds. Eastwards, judging by well- 
sections, the thickness of this division varies from 22 to 29 feet at Horb- 
ling, Billingborough, and Pinchbeck North Fen, but it increases to 33 
and 46 feet at Dunsby, and it is 35 feet at Bourn. At Swarby, south- 
west of Sleaford the thickness is stated to be 30 feet. II 
* Jukes-Browne, Geol. S.W. Lincolnshire, pp. 63, 64. 
t Ibid, pp. 140, 142, 146, 152. 
J Ibid. p. 147. 
Ibid., p. 64. 
j| Ibid., -pp. 140, 142, 147. The section recorded (Ibid. p. 67; by W. H. Holloway, 
in a brickyard at Little Humby, seems from the account of the strata to refer to the 
Upper Estuarine Series. 
