CHAPTER ONE 



THE GEOLOGY AND PHYSIOGRAPHY OF 

 THE CAMBRIDGE DISTRICT 



Edited by O. T.Jones, f.r.s. 



(With contributions by W. G. V. Balchin, A. G. Brighton, E. C. Bullard, 

 H. Godwin, O. T. Jones, W. V. Lewis, and T. T. Paterson) 



IN CAMBRIDGESHIRE AND THE SURROUNDING COUNTRY (FIG. I), 

 three broadly contrasted areas can be readily distinguished: (i) the 

 Chalk escarpment to the east and south-east; (ii) the western plateau; 

 and (iii) the Fenland occupying the northern part of the district. The area 

 is drained mainly by the Cam and the Ouse, which flow from the upland, 

 through the Fenland to the outfaU at King's Lynn. In the Fens they are 

 joined from the east by the Lark, the Little Ouse, and the Waveney, which 

 drain the Chalk region east of MildenhaU, Brandon, and Stoke Ferry. 



(i) The Chalk Escarpment, in the south and east, reaches its greatest height 

 (549 (t. above o.d.) near Therfield, south-west of Royston; it declines 

 north-eastward (to 400 ft. and below) towards Bury St Edmunds, and 

 descends to stiU lower levels farther north-east. This watershed is crossed 

 by three main depressions. One of these is followed by the Cambridge- 

 Liverpool Street branch of the L.N.E.R. from Chesterford to Newport; 

 the other by the Cambridge-King's Cross branch between Hitchin and 

 Stevenage; while the third lies some rrdles to the east, and joins the valley 

 of the Little Ouse with that of the Waveney. 



The escarpment is determined largely by the Chalk Rock which outcrops 

 near its brow ; the overlying Upper Chalk leads down to Eocene beds on 

 the fringe of the London Basin and is almost whoUy covered by glacial 

 drift. 



From the low ground occupied by the Gault around Cambridge, the 

 Chalk rises in gentle undulations to the brow of the escarpment (Fig. 4). 

 Among these undulations the effect of certain hard bands in the Chalk, 

 such as the Tottemhoe Stone (or BurweU Rock) and the Melboum Rock, 

 can be distinguished by minor escarpments and dip slopes. The general 

 character of this area is that of rounded ridges with intervening hollows 

 carrying, at the present time, little surface drainage. It is traversed by 

 shallow coombes (mainly dry valleys) wliich trend in a general north- 

 west-south-east direction. The Gogmagog ridge (rising to 222 ft.) is a 

 prominent feature near Cambridge (see Fig. 8). 



