INFERIOR OOLITE : PETERBOROUGH. 
203 
THICKNESS. DEPTH. 
Great Oolite 
Clay. 
Great Oolite 
Limestone. 
Upper Estuarine 
Series. 
Northampton 
Beds. 
Upper Lias 
Middle and 
Lower Lias. 
j*HVindstone and clay 
\ Blue clay and shells 
> Hard blue rock 
/ Hard brown clay 
\ Eock, hard clay and shell," 
f Sand and shells 
< Hard clay shells and sand 
[ Eock - 
Blue Clay - 
f Eock - 
< Clay with occasional layers 
and bands of stone 
FT. 
IN. 
FT. 
IN. 
10 


10 

20 

10 

30 

25 

55 

6 
o 
o 
61 
3 
7 
9 
69 

6 
6 
75 
6 
2 
6 
78 

85 

163 

3 

166 

- 262 4 
428 
Lower Estuarine 
Series. 
Northampton 
Sand. 
In Burghley Park the following beds were opened up during 
workings for ironstone : * 
FT. IN. 
Eemnants of Collyweston Slate. 
f Pale yellow sand - - 5 
< Blue clay, with vertical plant-mark- 
l ings - - - - 1 6 
/ Ferruginous beds. Ironstone with 
1 nodular band at base - - - 8 9 
Upper Lias Clay. 
Prof. Judd states that to the west of the Park, the Lower Estuarine clay 
overlying the Ironstone, has been dug for the manufacture of Terra-cotta. 
Here the clay (from one to four feet thick) is of a pale-blue colour and 
somewhat sandy, and according to Mr. Lumby, the proprietor, it is com- 
posed of almost pure silicate of alumina with a little free sand in very fine 
grains. Sandy lumps also occur in the mass, and are ground up with 
the clay in the mill. This admixture of the clay with fine sand is said to 
greatly improve its quality. Mixed with a very small quantity of the 
white clay from Poole, Dorsetshire, these clays of the Lower Estuarine 
Series make an excellent cream-coloured terra-cotta. Similar clay is found 
at other places in the same bed, and is largely used in the well-known 
terra-cotta works of Mr. Blashfield of Stamford.f 
* Sharp, Quart. Journ. Geol. Soc., vol. xxix. p. 273. 
t Judd, Geol. Rutland, pp. 103, 165. 
