462 Notices of Memoirs — British Association — 



This kind of evidence has chiefly accumulated since the meeting 

 of the Association at Ipswich in 1851 ; for of the 476 Suffolk wells 

 of which an account, with some geologic information, has been 

 published, only 68 were noticed before that year, all but two of 

 these being in a single paper. The notes on all these wells are 

 now to be found in twelve Geological Survey memoirs that refer 

 to the county. Number alone, however, is not the only point, and 

 many of the later records are marked by a precision and a detail 

 rarely approached in the older ones. It should be stated that in the 

 above and in the following numbers strict accuracy is not professed, 

 nor is it material. A slight error in the number of wells, one way 

 or the other, would make practically no difference to the general 

 conclusions. 



Now let us see how these records affect our knowledge of the 

 various geologic formations, beginning with the newest and working 

 downward. 



The Drift. — Under this head, as a matter of convenience for the 

 present purpose, we will include everything above the Chillesford 

 Clay. There is no need for refinement of classification, and the thin 

 beds that come in between that clay and the Driit in some parts do 

 not affect the evidence we have to deal with. 



As a matter of fact, it is only from wells that we can tell the 

 thickness of the Drift over most of the gi'eat plateau that this 

 formation chiefly forms; open sections through a great thickness of 

 Drift, to its base, are rare, except on the coast. 



There is often some doubt in classifying the beds, the division 

 between Drift and Crag being sometimes hard to make in sections 

 of wells and borings ; but fi'om an examination of the records of 

 these Suffolk sections that pass through any part of the Drift Series 

 (as defined above) we find that no less than 173 show a thickness 

 of 50 feet and upward, whilst of these S-i prove no less than 100 feet 

 of Drift, many reaching to much more. Of the two that are said to 

 show a thickness of over 200 feet and the one said to be more than 

 300 feet deep in Drift, we can hardly feel certain ; but such amounts 

 have been recorded with certainty as occurring in the neighbouring 

 county of Essex. 



These great thicknesses (chiefly consisting of Boulder-clay) show 

 the importance of the Drift, and the impossibility of mapping the 

 formations beneath with any approach to accuracy, on the suppo- 

 sition that the Drift is stripped off, as is the case in the ordinary 

 geologic map. The records also show the varying thickness of the 

 Drift, and how difficult it often is therefore to estimate the thickness 

 at a given spot. Sometimes the sections seem to point to the 

 existence of channels filled with Drift, such as are found also in 

 Essex and in Norfolk ; and it may be noted that in the northern 

 inland part of the former county, one of these channels has been 

 traced, though of course not continuously, for some eleven miles 

 along the valley of the Cam, and at one place to the depth of 

 340 feet (or nearly 140 below sea-level), the bottom of the Drift 

 moreover not bavins; been reached even then. A channel of this 



