116 
Mr. Lu nn on the Strata of Cambridgeshire , 
septaria together with rounded flints imbedded in the clay, the 
septae are formed of carbonate of lime and frequently of crystallized 
sulphate of barytes ; the fossil cornu ammonis is also abundant. 
In sinking one well in this parish, at a depth of about seventy 
feet, a bed of bituminous shale was cut through, of little more than 
an inch in thickness. 
It appears possible to form some guess of the height at which the 
water will stand in the wells which penetrate through the gait into 
the ferruginous sand ; for to meet with a spring the clay must be 
pierced. Supposing this nearly impervious bed to confine the water 
to the sand below, its first natural outlet is the termination of the 
gait and the commencement of the sand ; this takes place at Gam- 
lingay, and the level of the country being low, as might be ex- 
pected, water is here found in abundance ; the country is here one 
entire bog of variable breadth, but in some places of nearly a mile. 
Many parishes are without any real well, having only such as are 
sunk a short depth into the clay, and into these a small quantity of 
water oozing forms what is termed a land spring ; in Stow are three 
wells of which the general depth is about two hundred feet, but the 
water in each only rises to a certain uniform height, this (as near 
as can be estimated without having the exact level of the country) 
is the height of the outlet at Gamlingay bogs. 
The one of these last sunk is on rather higher ground than the 
others, and is to the sand 211 feet, to the present level of the water 
127 ; the case is much the same at Wimpole, but at Cambridge, 
Barton, and Hazlingfield, the water flows over the top of the well, 
although in some cases the sinking of a new well near to an old one*, 
lov/ers in a slight degree the level of water in the latter* 
