PLIOCENE PERIOD IN ENGLAND. 507 



melting probably escaped, passing out into the Trent basin instead 

 of into the Wash. 



The valley of the Cam, occupying as it does the space bare of 

 the Chalky Clay that extends through the south-west and centre of 

 Sheet 51, has evidently been all of it excavated by the ice of this 

 clay ; and I am informed that phosphatic nodules from the gault of 

 this valley-bottom occur in the Chalky Clay overwhelming the 

 island lying east of it, in Map 2. I shall attempt in the second part 

 of this memoir to show that the valleys of all the rivers running 

 through the area of the Chalky Clay to the Wash were entirely ex- 

 cavated by the ice which I have been describing, the rivers them- 

 selves having had no share in the process beyond removing (after 

 or as the country acquired its present inclination) part of the 

 gravels that first accumulated in them. 



Stage Y. The Period of the Purple Clay of YorJcshire and of 

 the Gravel e. 



Beyond those parts of Norfolk and Suffolk where the Cannon-shot 

 gravel and other spoil of the ice-water occur, the Chalky Clay pre- 

 sents that invariably bald surface of heavy land which forms the 

 principal wheat-growing area of England. Along the edges of the 

 valleys through it there occur small patches of gravel occasionally, 

 which rise to greater heights westwardly, until along the edges of 

 the formation nearest to the sea of the period we find it more gene- 

 rally overlain by gravel. The places where this occurs are those 

 where the ice at the close of the formation entered the sea. In the 

 north of Sheet 48, where the line of the sea-level of this period 

 begins to rise above that of the present day, we do not find this 

 gravel (e) overlapping the Chalky Clay so as to rest upon it, but only 

 as forming a sheet immediately below the lowest or plunging part 

 of the clay, in the manner shown by figs. I. and I. a, and here it 

 reaches the elevation of about 25 or 30 feet. As it extends due west- 

 wards, however, through Sheet 48 up the valley of the Stour, this 

 gravel covering continuously the wide valley-bottom gradually rises 

 in accordance with the westerly increment to an elevation of 60 feet 

 before reaching the boundary between this sheet and that numbered 

 47. Proceeding southward we find it continuous with c to the east 

 of the {Essex) Colne in the south of Sheet 48, while to the west of 

 that river it lies outside the flat- topped tablelands, covered with the 

 gravel c, to which the moraine did not reach. Separated from c by a 

 denuded slope of London Clay, it lies between it and that part of the 

 gravel which is marked / in fig. VI., and which skirts the coast in 

 Sheet 2, and touches in Clacton and Holland cliffs, at a low elevation, 

 the south centre of Sheet 48 before disappearing in the North Sea. 

 As it sweeps into the estuary of the Blackwater it is shown at the 

 eastern extremity of fig. YII. ; its elevation at ToUeshunt, which is 

 beyond the limit to which the moraine reached, corresponding with 

 that it reaches over the moraine at Braxted. Entering the valley of 

 the Blackwater this gravel there passes over the Chalky Clay where 

 this accumulated, after the change in the mode of deposition which I 



2m2 



