37 



The large outlying mass of Boulder Clay which has just been 

 descfibed as forming the upland between the valleys of the 

 Ouse and Cam must be looked upon as having once been con- 

 tinuous with that which rested against the chalk escarpment ; 

 the surface on which it lies forms an inclined plane, the base of 

 the clay being 220 feet high on the south and only 125 feet at 

 Lolworth, so that there is a fall of 100 feet in a northerly direc- 

 tion. It has nowhere to my knowledge been proved to be more 

 than 100 ft. thick, and its average thickness is probably much 

 less, except where it happens to fill up a pre-existing hollow. 



Thus at Scotland Farm, north of Hardwick, the well is said 

 to be 144 feet deep, but at least 50 of this must be Gault, for 

 that is the depth of the wells (through Gault) in the valley at 

 Dry Drayton. 



The same is probably the case at Old North Road Station ; 

 the well here is said to be 160 feet deep, but it is very impro- 

 bable that the whole of this is Boulder Clay, because in the valley 

 at Caldecote, only two miles to the N.E., about 60 feet of Gault 

 was pierced ; it would be safer therefore to assume that there is 

 a similar amount in the former well below the Boulder Clay, 

 especially as at Bourn, 1 mile N.N.E., in a well recently made, 

 only 60 feet of Boulder Clay was found above the Neocomian. 



[Mr Tomlison, C.E., of Cambridge, has since informed me of 

 a well at Hatley St George, which is said to have pierced the 

 following beds : — 



feet 



« Gault" (Boulder Clay) 120 



Gravel 28 



Gault (probably true Gault) 22 



Sands (Lower Greensand) 30 



200 



This is interesting as showing gravel beneath a great thick- 

 ness of Boulder Clay, but it is probably a local phenomenon, and 

 cannot be taken as indicating the existence of a Middle Drift, 

 or as giving the normal thickness of Boulder Clay. 



The Bev. O. Fisher informs me that water was obtained at 

 Comberton vicarage by piercing the Boulder Clay, a supply 



