PLIOCEBTE PEEIOD IIT ENGLAND. 503 



of the Chalky Claj^ below its present line*. When the position of 

 the Chalky Clay in the Norfolk and Suffolk valleys had not been 

 detected, particularly the remarkable instance disclosed by the Nor- 

 wich Sewer-works, the theory of the gradual erosion of the valleys 

 by the action of a river from higher to lower levels seemed plausible, 

 and the deposition of the gravels in a series extending from a higher to 

 a lower level seemed j)rimd facie a reasonable hypothesis, as, whether 

 true or not, it may still appear in areas outside the action of the 

 newer Pliocene land-ice ; but such an explanation seems to me quite 

 to fail before the evidences connected with the East- Anglian valleys, 

 which the researches of the past 10 or 15 years have disclosed, and 

 we must, I submit, seek other explanations. 



The flood-waters produced by the ice-melting, which I have 

 described so far as I have traced it, seem to me to supply this ex- 

 planation, were it not that there would, without some other, be as 

 much difficulty in supposing these valleys, if the escape were free, 

 filled with water from the ice melting up to this high level, as there 

 would from the snow-melting of an ordinary arctic or subarctic land 

 surface. Nothing, it seems to me, but an impediment to the free 

 escape of it could have kept the water at levels necessary for the de- 

 position of gravel in the otherwise inconsistent way in which we find 

 it there, and this impediment the unequal melting of the ice filling 

 the valleys seems to me to supply. 



For instance, in the valley of the Yare, at Norwich, a little west 

 of the line of fig. IX., the valley-gravel rises to a height of about 

 50 feet above the river, and is seen in the railway- cuttings carried 

 through it, near the Norwich (Thorpe) station ; but though at a 

 much lower level than this, the clay d in the valley-bottom in 

 fig. IX. shows no trace of gravel on it. Numerous instances of the 

 like kind occur in this valley and in others of this part of England ; 

 and at Tharston in the valley of the Tese, a tributary of the Yare, 

 a tumultuous accumulation of this gravel contains strips of the Chalky 

 Clay imbedded in it. 



The similar infilling of the Waveney valley by alluvium to that 

 of the Yare, and up to greater height, as regards the floor of the 

 Pliocene formations, conceals, as I have said, the evidences of these 

 interglacial phenomena to a great extent there ; but the chief part, 

 if not all, of the gravel in the bottom of that valley appears to 

 me to belong to this glacier -ice-melting, and not to the river. It 

 forms an extensive sheet for some miles on both sides of Bungay, 

 rising only some 10 or 15 feet above the alluvium ; and an extensive 

 sheet of it fills the valley of the Little Ouse, patches also occurring 

 on the higher slopes f. 



^ During the depression of the east of England below its present level, which 

 I shall, in the second part of this memoir, show took place during the forma- 

 tion of the Cyrena brickearth /", river-gravel may, however, have formed in 

 these valleys, and be mixed up undistinguishably with e' in their bottoms. 



t So far as land or freshwater shells may occur in these gravels (which it 

 would seem, from a statement by Mr. Plower at p. 50 of the 23rd vol. of the 

 Quart, Journ., has not yet been the case) we must remember that the Hoxne 



