598 ME. P. G. H. BOSWELL ON THE [Dec. 1913, 



emphasized in the south of the county by the transgression of the 

 Tertiary strata westwards over successively lower zones of the 

 Chalk. 



Naturally, the larger valleys cut hack these Chalk-surface con- 

 tours, and these take either a sharp V-form, or a closed oval form 

 where a channel exists ; but the small scale of the map prevents me 

 from showing these anomalies, only the chief borings in each valley 

 being inserted. The figures, in all cases, refer to the position of the 

 top of the Chalk with reference to Ordnance Datum, the negative 

 sign referring to depths below O.I). In the western part of the 

 county the Drift rests directly on the Chalk ; but in the eastern 

 portion the borings show Eocene and Pliocene strata between. As,. 

 however, it is often difficult to fix the exact base of the Drift in the 

 well-section when it overlies Crag and Eocene deposits, the upper 

 surface of the Chalk has been recorded in each case ; it can be 

 placed with certainty, and serves the required purpose equally welL 

 The data are, nevertheless, insufficient to yield an accurate hypso- 

 metrical map. In this way some striking facts are brought to 

 light. The existence of buried channels of the Drift at Glemsford, 1 

 Brettenham, 2 Ipswich, 3 and possibly "Woodbridge 4 has previously 

 been pointed out. Similar ones have been described on the west of 

 the area at Hitchin 5 ; in the Cam Valley in North-West Essex 6 ; 

 at Bishop's Stortford 7 ; and at Sandy in Bedfordshire. 8 Examination 

 of the well-records shows that each one of these radiating 

 Suffolk valleys of any size contains a buried channel. 

 The evidence for these channels will now be considered in 

 detail. 



(a) St our Y alley. — The remarkable thickness of Drift met 

 with in the boring at Glemsford, north of Sudbury, has been 

 frequently commented upon. The boring was begun at 123 feet 

 O.D., and, after passing through 471 feet of Drift, reached the 

 Chalk. It is not necessary to reprint full details, but the chief 

 groupings were : — Gravel and sand 51 feet, Boulder Clay 218 feel r 

 sand and gravel with flints 201 feet, Chalk 40 feet. This section 

 makes the level of the Chalk —348 feet O.D., while at neigh- 

 bouring places it crops out at a level considerably above O.D. (for 

 instance: Clare + 151 feet, Sudbury -4- 110 to 120 feet). Moreover,, 

 as Mr. Whitaker points out, the section begins at some depth below 

 the great mass of Boulder Clay, which on the plateau near by 

 reaches a height of more than 250 feet O.D. 



(b) Brett Valley. — At Eelsham, near the head of the valley, 

 the Chalk surface occurs at 120 feet O.D., but at Brettenham and 



1 Whitaker, 1906 (21) p. 58. 2 Ibid, p. 32. 3 Ibid. p. 77, etc. 



* Whitaker, 1903 (20) pp. 36 & 47. 



5 W. Hill, 1908 (23) p. 8, & 1912 (35) p. 217. 



6 Whitaker, 1890 (13) p. 333. '' Irving, 1897 (16) p. 224. 

 s J. Hopkinson, Q. J. G. S. vol. lix (1903) p. 49 (discussion). 



