616 MR. P. G. H. B0SWELL ON THE [Dec. 1913, 



portions of Suffolk rivers and turned them into wide open estuaries. 

 The navigation-channels in these estuaries give a clue to the 

 position of the river itself. The rivers, reduced in bulk, with a 

 lower gradient, 1 have deposited small flood-plains of alluvium 

 between their old terrace-outlines, and are now engaged in mean- 

 dering to and fro in these alluvial flats. Where they touch their 

 old terrace, villages have been built. As previously pointed out, 

 the small streams now occupying these wide open valleys are quite 

 out of proportion to them, and either indicate a good old age 

 (which is not altogether supported by other evidence), or that there 

 has been some interference with their development : namely, that 

 caused by the ice-sheet and valley-glaciers, and a depression which 

 followed the glaciation. 



Minor changes have taken place since this last subsidence of the 

 area, and are taking place to-day, being mainly due to the southward 

 tidal drift down the Suffolk coast. This, by damming up river- 

 mouths with shingle, and permitting silting-up to take place, is 

 either tending to form broads, as described by Prof. J. W. Gregory 

 for Norfolk, or diverting the mouths of the rivers southwards. 

 Such deflection is exemplified by the classical case of the Aide, 

 but can be observed to be in process with smaller streams, as well 

 as with the Orwell and Deben. 



VII. Conclusions. 



(1) The valley-system of Southern and Eastern Suffolk is radiating 

 in character from the watershed paraUel to the Chalk escarpment 

 in the north-west, the rivers being largely consequent but partly 

 subsequent in form. The valleys are wide and graded, all angu- 

 larities having been worn off, and are carved out of all proportion 

 to the size and number of the streams that now occupy them. 



(2) On the evidence of the excavation of Red, Norwich, or 

 Chillesford Crags, respectively, by the rivers, the valleys (though 

 they may have been etched earlier) are post-Chillesfordian in age. 

 By analogy with the Waveney and Norfolk rivers, they may be 

 younger than the Contorted Drift (Lower Glacial). 



(3) Upper Boulder Clay lies persistently in the valleys, there is- 

 Glacial buttressing on projecting spurs, and in each main valley 

 there is a channel filled with Drift. On these three counts the 

 valley-system is older than the Upper Glacial deposits. 



(4) There is a similarity of form and origin between the buried 

 channels and the Continental Fohrden, which are admittedly due 

 to sub-glacial drainage. 



(5) The present river-system is recovering from a state of 

 arrested development, due to the glaciation of the area (and conse- 

 quent overloading of the valleys with debris) and the subsidence 

 which followed it. 



1 That of the Gipping is, in its portion from Uaughley to Needham, 1 in 

 713, and in its lower portion (Needham to Ipswich), 1 in 1003. 



