464 Notices of Memoirs — British Association — 



persistent division), tliongh here and elsewhere it is possible that the 

 underlying Thanet Beds are thinly represented. It is noteworthy 

 that at both these places, where the Lower London Tertiaries are 

 thick, they are also at a great depth, beginning at 252| and 218 feet 

 respectively, which looks as if, like the Crag, they thickened in their 

 underground course awaj'^ from the outcrop. 



The important evidence given by these wells, however, is not as 

 regards thickness ; it is to show the underground extent of the older 

 Tertiary beds, beneath the great sheef- of Crag and Drift that pre- 

 vents them from coming to the surface north-eastward from the 

 neighbourhood of Woodbridge. It is clear that over this large tract 

 we can know nothing of the beds beneath the Crag otherwise than 

 from wells and borings ; and, until these were made, our older 

 geologic maps cut otF the older Tertiary beds far south of the parts 

 to which we now know that they reach, though hidden from our 

 sight. No one, for instance, would have imagined many years ago 

 that at South wold the Chalk would not be touched till a boring had 

 I'eached the deptli of 323 feet, or some 280 below sea-level, nor that 

 at Leiston those figures would have been about 297 and 240. 



It is from calculations based on the levels of the junction of the 

 Chalk and the Tertiary beds in many wells that the line engraved 

 on the Geological Survey map as the probable boundary of the latter 

 beds under the Crag and Drift has been drawn. From what has 

 gone before, however, as to the great irregularity in the thickness 

 of the Drift, it is clear that this line must be taken only as approxi- 

 mate, and open to correction as further evidence is got ; albeit the 

 junction of the Chalk and the Tertiary beds is found to be here, as 

 elsewhere, fairly even, along an inclined plane that sinks towards 

 the coast. 



Cretaceous Beds. — Though the Chalk is reached by very many 

 wells, yet w^e get less information about it, by reason of its great 

 thickness. Moreover, the great amount of overlying beds in many- 

 cases is a bar to deep exploration. 



Of our Suffolk wells there are forty which go through 100 feet or 

 more of Chalk. Of these twenty go through 200 feet or more, half 

 of these to 300 or more, and again half of the ten to 400 or more, 

 a very exact piece of geometric progression, or more strictly, retro- 

 gression. Although two wells pass through the great thickness of 

 more than 800 feet of Chalk, yet neither of them gives us the full 

 thickness of the formation ; for the 816 feet at Landguard Fort do 

 not reach to the base, whilst the 843 (or 817) feet at Combs, near 

 Stowmarket, do not begin at the top. 



As in no case yet recorded has the Chalk been pierced from top to 

 bottom in Suffolk (a defect that will be supplied during this meeting 

 by the description of the Stutton boring), that is to say, no boring 

 has gone from the overlying older Tertiary beds to the underlying 

 Gault, we must now, therefore, cross the border of the county to get 

 full information as to the thickness of the Chalk ; and we have not 

 far to go, for the well-known Harwich boring passes through the 

 whole of the Chalk, proving a thickness of 890 feet. It is almost 



