a 
TRANSACTIONS OF THE SECTIONS. 43 
is full of characteristic fossils, such as Ostrea deltoidea, Gryphea virgula, Ichthyodo- 
rulites, reptiles’ bones, &c. In other places, however (e. g. at Great Gransden and 
Elsworth), the lower greensand appears to overlap the Kimmeridge clay and rests 
immediately on a clay full of Oxford clay fossils, such as Gryphea dilatata, &c. 
In this respect the relations of the lower greensand to the inferior formations is only 
analogous to what is so often seen on the south coast of England. 
5. Coral Rag or Middle Oolite.—It is well known that this formation, of a great 
thickness on the south coast of England, gradually thins off in its range towards the 
north, and comes to an edge in Buckinghamshire. In its further range towards the 
north-east, for more than 100 miles, it almost entirely disappears, and» the Oxford 
clay and Kimmeridge clay are brought together without the intervention of any 
stone bands to break the uniformity of the surface. The consequence is, that they 
form a great plain occupying a part of Cambridgeshire, Norfolk, and Lincolnshire. 
To this remark there is one striking exception ; for at Upware, about eight miles be- 
low Cambridge, a low ridge, extending about a mile in length and a few hundred 
yards in breadth, rises out of the fen-lands. It is formed by a saddle of most cha- 
racteristic coral rag, with many characteristic fossils. The author conjectures that 
this elevation was effected by the same disturbing forces which produced the great 
fault, above noticed, at Ely. This deposit is not exposed to its base, but cannot, it 
is thought, be more than fifteen or twenty feet thick, and it is certain that it does 
not form a continuous band concealed under the fens, as several wells have been sunk 
(between Cambridge and Lynn) through the Kimmeridge clay into the Oxford clay 
without passing through any beds which bore a resemblance to the coral rag. 
The accompanying section will explain the above short description. 
Section from the chalk hills, near Burwell to the great outlying ridge of lower 
greensand near Haddenham. 
Hills E. of River Chalk Hills 
N.W. Haddenham. Cam. Upware. near Burwell. S.E. 
1 
6. Lower chalk. ec. Upper greensand. . Galt. 
Jf. Kimmeridge clay. g. Coral rag. h. Oxford clay. 
e. Lower greensand, 
On the right-hand side of the section, c d ef are buried under the marsh land. 
But to the west of the Cam f (Kimmeridge clay) is worked in several pits; and 4 
(Oxford clay) breaks out on the north-west side of Haddenham ridge; but on that 
side no trace of the coral rag has been discovered. 
6. Oxford Clay.—This formation occupies by far the largest portion of the great 
Bedford Level, and is of very great but unknown thickness. Its western boundary 
is defined by the outcrop of the great oolite, and does not belong to the geology of 
the neighbourhood of Cambridge. Its eastern boundary is very ill defined, often 
passing under marsh lands where the subsoil is concealed from the view. At Great 
Gransden and Elsworth, as stated above, it breaks out from beneath the lower green- 
sand. All the low lands between Coningtor and St. Ives are composed of it. The 
fen lands extending from Cottenham to Ely are on the Kimmeridge clay; and in 
consequence of the wpcast fault, which has produced the great outlier of Ely and 
Haddenham, the Oxford clay is thrown more towards the north-west, so that its 
upper beds crop out on the north-west side of the ridge, as appears in the preceding 
section. 
Such are the principal facts connected with the stratification of the country near 
Cambridge, and the localities where they are best exhibited may be examined a day’s 
excursion from Cambridge. 
Irregular overlying Deposits, not now in progress of formation and unconnected with 
the present action of the Surface Waters. 
1. Great Brown Clay.—This seems very closely to resemble the ¢ill of Scotland, 
