:> The Physiography of Cambridgeshire 



The full significance of the various features will 1 

 when the reader has studied the section of this guide which 

 is concerned with an account of the geology of the county, 

 but it is necessary to refer at this point to the general characters 

 of the geological formations underlying the area. 



Of the three important areas into which the county is 

 structurally divisible, the first-mentioned only can be said t<> 

 possess a form which is the direct outcome of the influence of 

 the stratified rocks which underlie it. In the second area the 

 underlying strata apparently exercise little effect upon the 

 character of the surface features. Chalk, Gault clay, Greensand 

 and Jurassic clays alike rise to a plateau-like surface, which 

 for a distance of fifteen miles does not depart from the two 

 hundred and twenty foot contour to an extent of more than 

 ten or a dozen feet. This plateau is much dissected by agents 

 of denudation, and the shape of its contours is distinctly 

 remarkable. The third area, the Fenland, owes its position 

 to the existence of a great thickness of slightly inclined 

 Jurassic clays beneath it, but the actual form and flatness of 

 the area has been determined, firstly by denudation of these 

 clays, probably as the combined effect of subaerial and marine 

 action, and secondly by deposit of silt and by plant-growth. 



The more ancient rocks which exist in the county belong 

 to the Jurassic and Cretaceous systems. As the strata dip 

 gently in a direction a little south of east, the older (Jurassic) 

 rocks occupy the northern and western portions of the county, 

 while the southern and eastern parts are occupied by the 

 newer (Cretaceous) rocks. The Jurassic rocks consist chiefly 

 of clays, and are therefore marked, on the whole, by low 

 ground. 



The nature of the Cretaceous rocks varies. The lowest 

 group consists of sands ; these are succeeded by clays which 

 crop out to the east of the sands, and east of the clays lie 

 the various members of the chalk. 



The superficial accumulations which cover the moiv ancient 

 rocks are very variable. The principal, in addition to ordinary 



