

The Fenland 5 



or is absent. An exception to this is seen when the ground 

 is occupied by uncovered Chalk or .Greensand, each of which 

 determines the existence of its peculiar flora. Neither, 

 however, exerts much influence upon the form of the plateau, 

 which exists as high land because it forms the watershed 

 between the Ouse and Cam, though the exact conditions 

 under which the plateau structure was brought about have 

 yet to be determined. 



The district is flanked on the north-east by a great finger 

 of river-gravel which extends out into the Fen basin along 

 the line of the Huntingdon Road between Girton and Fen 

 Stanton. 



(iii) The Fenland. Generally speaking, the county to the 

 north of a line joining Over and Newmarket is occupied by 

 fen. 'Islands' project here and there, as at Ely, Upware, 

 and March, but these form only a very small proportion of 

 the whole tract. The Fenland occupies a wide-spread hollow 

 which was excavated in pre-glacial times, for Boulder-clay is 

 often found beneath the fenland accumulations. Its width 

 is due to the gentle arching over of the belt of Jurassic Clays, 

 the erosion of which has determined the existence of the 

 fenland tract. The floor is probably not a very even surface, 

 but silt deposited by the sea, mud brought down by the rivers, 

 and vegetation growing upon the surface have built up the 

 area to a very uniform plain not more than a foot or two 

 above mean- tide level. The Fens, therefore, in pre-Roman 

 times had become " a swampy plain interspersed with drier 

 places, and with deep morasses," and in the parts near the sea 

 this was liable to be flooded by high tides. 



The tract is largely occupied by peat in the south, and 

 by silt in the north: the latter occupies a strip of country 

 about twelve miles in width just south of the Wash, and 

 extends southwards as a great triangular wedge with its 

 apex near Littleport. 



The conditions of the Fenland have greatly altered during 

 historic times as the result of human interference. The 



