42 REPORT—1845. 
twenty feet thick. It is composed of beds of sand and hard sandstone, sometimes 
slightly calcareous, and is generally of a yellowish or rusty-brown colour, resembling 
the upper beds of the formation seen on the south coast of England. Its fossils are 
few in number and obscure, being composed of ferruginous mineralized fragments _ 
of dicotyledonous wood, of fragments of shells, and bones of fishes. Good charac- 
teristic fossil fishes have however been found in the formation near Lynn. As it is 
pervious to water, is imbedded between two impervious strata of clay, and crops 
out (on the confines of Huntingdonshire and Bedfordshire) at a higher level than 
the surface of the galt at Cambridge, it readily affords a supply of water to the 
Artesian wells, as appears by the accompanying section*. 
The most remarkable exhibition of the lower greensand is seen in an outlying 
ridge (surrounded by low fen-lands and forming the true Isle of Ely) extending from 
Ely to Kilrow, west of Haddenham. The ridge cannot be accounted for by the re- 
gular rise of the strata towards the west, combined with a subsequent denudation ; 
but has been produced by a fault elevating the ridge above the mean level of the 
surrounding fens. This has been satisfactorily proved by the recent cuttings for the 
railroad, which expose the chalk mar] in situ at the base of the hill composed of Kim- 
meridge clay and lower greensand. This chalk, to be on its true geological level, 
ought to be about 150 feet above the top of the ridge. It is presumed, therefore, 
that there is on the south-east side of the ridge a fault or upcast of about 150 feet, 
as appears by the accompanying sections. 
1st section exhibited at the brown-clay pits at Ross Hill on the N.E. side of Ely. 
S.E. N.W. 
a. Brown-clay with large boulders. 4. Lower chalk, shaken and slightly contorted. 
c. Lower greensand. d, Kimmeridge clay. 
2nd section, below the preceding, laid bare by the cuttings of the new railroad. 
S.W. N.E. 
a. Brown-clay. 6. Chalk marl or lower chalk. d. Kimmeridge clay. 
In this section, which is at a lower level, the lower greensand does not appear. 
The author thinks from the appearance of the sections that the fault took place 
immediately before the deposit of the brown clay. 
4. Kimmeridge clay.—This deposit is best seen in the great clay-pits near Ely. It 
* West byS. Sand-pits near Gamlingay. Cambridge. 
a, Overlying brown clay (Till). 6, Chalk marl, ce. Upper greensand. d. Galt. 
e. Lower greensand. jf. Kimmeridge and Oxford clay. Thickness unknown. 
The bore-holes at Cambridge through d. of the section admit the ascent of the water which 
enters, at a higher level, by the outcrop of the sand e. 
