4 The Physiography of Cambridgeshire 



chiefly of scarps facing a little north of west, and of dip 

 slopes facing south of east. The various divisions of the 

 Chalk form scarps of different degrees of importance, the 

 principal being those of the Lower Chalk, which is well 

 at Cherryhinton, and of the Upper Chalk seen near Balsham. 

 The shape of the hills is that of typical chalk downs, namely 

 rolling undulations, and where the Boulder-clay has been 

 removed the vegetation is also characteristic, though the flora 

 of low-growing plants has been greatly modified as the result 

 of cultivation. Until the beginning of the nineteenth century 

 the ground was largely occupied by short turf, but most of 

 it is now under the plough and the character of the original 

 turf is only preserved here and there, as on the Fleam Dyke and 

 the Devil's Dyke. Lines of beech-trees mark the boundaries 

 of the chalk. A good deal of the Boulder-clay land has been 

 planted with trees, and the chalk country as a whole is quite 

 well wooded and is distinctly picturesque. The district, as 

 above noted, is drained by a series of streams flowing in a 

 direction opposite to that of the dip of the strata. Many 

 dry valleys show that the superficial drainage was once more 

 extensive* : now, the bulk of the rain which falls is absorbed, 

 and much of it is given out by a series of springs which mark 

 the outcrop of the impervious Chalk-marl at the base. 



(ii) The Western Plateau. This is, geologically speaking, 

 the most complicated of the Cambridgeshire districts. It 

 is mostly covered with a thin capping of Boulder-clay, but 

 in places the Boulder-clay is of great thickness. Occasionally 

 the underlying rock is exposed on the low ground. 



The district is bounded on the south-east by the outcrop 

 of Gault along which the Rhee flows. It includes the Chalk 

 outliers of Madingley and of the Haslingfield-Wimpole region, 

 with the large tract of Gault to the west of them. The Lower 

 Greensand from Gamlingay to Lolworth and the Upper Jm, 

 clays to the west of that also underlie this plateau. Most of 

 the rocks are therefore clays, and the character of the country 

 is much the same whether Boulder-clay occurs at the surface 



