Vol. 69.] AGE OF THE SUFFOLK VALLEYS. 597 



to lie on the flanks of the valleys. Nowhere in the numerous 

 sections on the plateau have such anomalies heen observed (al- 

 though one or two hypothetical sections have been drawn on quite 

 insufficient evidence), neither do the well-records there show 

 anything but a normal state of affairs. The fact that marked 

 disturbance occurs only in the valleys, seems, therefore, to be more 

 than mere coincidence. It is probable that the ice-sheet which 

 produced the Chalky and Clialky-Kimeridgic Boulder Clay of the 

 plateau rolled upon a bed of Glacial Sand and Gravel, producing 

 the generally flattened character of the latter deposits. 



The conclusion drawn, therefore, from a study of the spurs of 

 the Suffolk valleys is that the pre-Glacial or early Glacial 

 contours of the area were, in the main, much as they 

 are at the present time. 



V. Evidence of Age from Well-Borings, etc. 



The records of the strata shown by over 600 borings in Suffolk 

 and on the borders of Essex and Norfolk have been analysed. 

 Many of these, for various reasons (not the least of which is the 

 lack of information as to altitude and exact situation of the boring), 

 were of little or no use, but over 200 were accurately plotted 

 •on a map of Suffolk (PI. LIV). The siies of most of these borings, 

 especially the critical ones, have been visited, and in many cases 

 the exact site and the height above Ordnance Datum have been" 

 obtained where they were previously missing in the records. The 

 production of a sub-Drift contoured map was at first attempted, but 

 was abandoned on account of the necessarily arbitrary grouping of 

 the strata in the well-borings, etc., where Glacial beds of sand, 

 loam, and clay were resting on Crag sand ( = decalcified Crag) and 

 Eocene clays and sands. 1 No geologist having been present when 

 most of the borings were made, it appears that the only bed the 

 level of which can be widely relied upon is the Chalk. On the 

 map (PI. LTV) the approximate contour-lines for the Chalk surface 

 on the plateau are inserted, in order to bring out the anomalous 

 levels in the valleys where buried channels occur. The noteworthy 

 ' crowding-up ' of the contours in the south and east of the county 

 is explained when the present extent of the Eocene deposits is 

 marked upon the map. The gradient of the Chalk surface where it 

 •crops out, or is covered only by Drift, is closely 7 feet to the mile ; 

 but, where covered by Eocene deposits, it dips almost 30 feet to the 

 mile. 2 The unconformity of the Eocene upon the Cretaceous is 

 well brought out, when it is noted that the dip of the Chalk zones 

 is about 15 feet to the mile. This unconformity is further 



i Tn a recent letter Mr. F. W. Harmer tells me that some years ago he 

 spent much time in trying to work out the sub-Glacial contours of Norfolk by 

 the same method, but without success. 



2 Boswell, 1913 (37) p. 18. 

 Q. J. G. S. No. 276. 2 r 



