GREAT OOLITE SERIES : ALW ALTON. 415 
Prof. Judd remarks that " There are several points of some 
interest in connexion with this section. In the first place the 
'ironstone junction-band' at the base is double, this being how- 
ever merely a local variation. And, secondly, the character of 
the lower, white, sandy, and argillaceous beds of the Upper 
Estuarine Series, is such as to forcibly suggest that they may 
have originated in the denudation of limestone beds like those 
on which they repose ; the soluble calcareous constituents 
having apparently been removed, and the remaining fine- 
grained materials sorted in moving water. A similar origin has 
been assigned to other fire-clays of analogous character." 
The occurrence of sandy beds graduating down into the 
Lincolnshire Limestone is a noteworthy and unusual feature. No 
fossils are recorded by Prof. Judd, but it is possible (having 
regard to the unconformity with the beds above), that we have 
here somewhat higher portions of the Lincolnshire Limestone 
than are elsewhere shown. 
Prof. Judd mentions that at Castor the oyster-beds of the Great 
Oolite Limestone are seen, and on Castor Heath the Limestone 
assumes the form known as Alwalton Marble, greatly resembling 
some of the flaggy beds of the Forest Marble of the south of 
England. The beds "which are seen at several points about 
Water Newton, can be traced between that point and Alwalton, 
at which latter place they are well exposed in the railway-cuttings 
and old marble-pits. The steep escarpment of the Alwaiton 
Lynch is formed by the limestones and oyster-beds of the Great 
Oolite, overlying the variegated sandy clays of the Upper 
Estuarine Series. The beds are well seen in the road leading 
from the village down to the Nene. The Alwalton Marble was 
formerly dug all along the Alwalton Lynch, but the whole of the 
pits are now closed. The hard, blue, shelly limestone was found 
to take an excellent polish, but does not appear to have been very 
durable." 
a About Milton Park a number of wells showed the beds of the 
Great Oolite Limestone to vary from 10 to 20 feet in thickness. 
There is a small pit in the oyster-beds in Thorpe Park." 
"At Orton (or Overton), near Peterborough, a well gave the 
following succession of beds " : 
Cornbrash. 
Great Oolite Clay - .... 13 to 14 feet. 
Great Oolite Limestone - - - 17 feet. 
Upper and Lower Estuarine Series - 39 feet. 
Ironstone-rock (Northampton Sand). 
e> In the admirable exposures of the Great Oolite in the rail- 
way-cuttings at Bottlebridge, near Orton, the late Dr. Porter 
collected large numbers of very interesting fossils."* Many 
specimens were also obtained by Prof. Judd from Ailsworth, 
near Castor. Lists of fossils from the Great Oolite of this 
neighbourhood have been published by Sharp.f 
* Judd, Geol. Rutland, pp. 207-209 ; and Porter, Geology of Peterborough, 1861. 
| Quart. Journ. Geol. Soc., vol. xxix. p. 279. 
