Yol. 69.] AGE OF THE ST/FFOLE VALLEYS. 585 



II. The Eakliee, Limit of Age. 



Suffolk consists of a plateau-type of country sloping south-east- 

 wards from a culminating height of a little over 400 feet O.D. near 

 Ched burgh, 6 miles south-west of Bury St. Edmund's, and forming 

 a series of low cliffs on the coast. The greater part is at an eleva- 

 tion of 100 to 200 feet O.D., and the plateau is much cut up by a 

 large number of streams tributary to the rivers already mentioned. 

 Most of these excavations into the plateau are totalty out of propor- 

 tion to the quiet meandering brooks which now occupy them. The 

 sides have generally a low gradient (1 in 40 or 50), with the result 

 that the broad valleys expose the Pliocene, Eocene, and Chalk strata 

 under the mantle of Drift. An idea of the gradient is obtained 

 when it is seen, for example, that the London ('lay (some 30 feet or 

 less thick) in the southern valleys gives an outcrop measuring 

 nearly a mile in width. 



The Waveney Valley cuts down through the Contorted Drift and 

 Crag Beds to the Chalk, sections exposed at various points showing 

 that the valley is therefore later in age than the Contorted Drift. 1 

 The series of small streams between the Waveney and the Aide, and 

 also the latter river itself, cut through the Crag Beds (Chillesford 

 Beds and Norwich Crag), and on direct evidence are of post- 

 Pliocene age. The Deben flows in a valley which exposes chiefly 

 Bed Crag and London Clay, while the Gipping, Brett, and Stour 

 valleys are excavated through Bed Crag, London Clay, and Lower 

 London Tertiaries into the Chalk. Exposures of the Lower Boulder 

 Clay or Contorted Drift have been described from time to time as 

 occurring in the southern half of Suffolk, but I am of opinion that 

 it does not extend so far south. It was described by Wood & 

 Harmer as cropping out in the form of mounds through the 

 so-called ' Middle Glacial Sands.' ~ S. V. Wood, Jun., held the view 

 that it underlay parts of the high land of Suffolk; but of this 

 there is no evidence whatever, either in the field or from borings. 

 (Mr. Harmer tells me that he was never quite satisfied about 

 several of the recorded occurrences.) The consideration of most of 

 the localities is not necessary here, but it is clear that the majority 

 of the exposures are in the brickearths, which lie usually as 

 lenticular masses in basins of the sand and gravel, and thus are 

 younger, being probably connected with the ' wash-out ' waters 

 from the oncoming ice-sheet which produced the Upper Boulder 

 Clay. The officers of the Geological Survey were usually dis- 

 inclined to commit themselves to any definite statement regarding 

 the age of these loams : but in a few cases, as, for example, the 

 consideration of certain loams occurring on valley-flanks near 



i At, the brickfield, 1 mile south of Beccles, at 100 feet O.D., 30 feet of Chalky- 

 Kimeridgic Boulder Clay overlies 25 feet + of Contorted Drift, separated by a 

 few feet of sand. East of the town the Upper Boulder Clay rests in the 

 valley on Chillesford Beds at less than 30 feet O.D. See also F. W. Harmer, 

 1910(29) p. 130. 



2 Wood & Harmer, 1877 (7) p. 80. 



