TRANSACTIONS OF SECTION C. 667 



some geologic infovmation, has been published, only 6S 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. 

 Numbei' 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 the wells, one way 

 or the other, would make practically no ditiereiice 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 relinement of 

 classification, and the thin beds that come in between that clay and the Drift 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 great plateau that this formation chieflj^ 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 from 

 an examination of the records of these Suffolk sections that pass through any part 

 of the Drift Series (as defined above) wo find that no less than 173 show a thick- 

 ness of 50 feet and upward, whilst of these 34 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 i'OO feet and the one otlier said to be more than 300 ieet deep in Drilt, we can 

 hardly feel certain ; but such amounts have been recorded with certainty as occur- 

 ring 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 stipposition that the Drift is stripped off, as is the 

 case in the ordinnry 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. Suuietimes the sections seem to point to the existence of channels 

 tilled with Drift, such as are found also in Esse.x 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 11 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 having been reached even then. A 

 channel of this sort seems to occur close lo us, in the midst of the town of Ipswich, 

 where, by St. Peters, one boring has pierced 70 feet of Drift, and another 127, 

 in ground but little above the sea-level. 



As the Drift sands and gravels, that in many places occur below the Boulder 

 Clay, often yield a fair amount of water, the proof of their occurrence and of the 

 thickness of the overh ing clay is of some practical good. 



The Crag. 



On this geologic division we have a less amoimt of information, as would be 

 expected from the fact that it is not nearly so widespread as the Drift, and this 

 information is confined to the Upper, or Red, Crag, the Lower, or Coralline, Crag 

 occurring only over a very sooall area, and no evidence of its underground exten- 

 sion being given by wells. 



What we learn of the Red Crag, however, is of interest, several wells having 

 proved that it is far thicker underground than would have been supposed from 

 what is seen where its base crops out. One characteristic, indeed, of this sandy 

 deposit, in the many parts where it can be seen from top to bottom, is its thinness, 



