TRANSACTIONS OF SECTION C. 669 



Of our SiifiTolk wells tliere are forty which go through 100 feet or more of 

 Chalk. Of these twenty go through 'iOO 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, retrogression. Although two wells pass through 

 the great thickness of more than 800 feet of chalk, yet neither of them gives us 

 the full tliicliness 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 iu 

 Suffolk (a defect that will be supplied during this meeting by the description of 

 the Stutton boring), that is to sav, no boring has gone from the overlying older 

 Tertiar}' beds to the underlying Gault, we must now, therefore, cross the border 

 of the county to get full ibformation 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 certain, indeed, that this 

 should be given as a few feet more, for the 22 feet next beneath, which have been 

 described as Gault mixed with Greensand, is probably in part the green clayey 

 glaiiconitic base of the Chalk Marl. We may fairly add for this another 5 feet 

 ("as also in the case of the Combs boring), and may say that, in round numbers, the 

 Chalk reaches a thickness of about 900 feet in the south-eastern part of Suffolk. 

 Toward the northern border of the county it is probably more, as the deep boring 

 at Norwich pa-sses through nearly 1,160 feet of Chalk, and that without beginning 

 at the top of the formation. 



Of our recorded Suffolk wells only three reach the base of the Chalk, at 

 Mildenhall, Culford and Combs; consequently we have little knowledge of the 

 divisions of the Chalk. These divisions, indeed, are of comparatively late inven- 

 tion, having been evolved since the publication of many of the deep sections that 

 have been referred to. 



If the Upper Chalk at Harwich goes as far down as tlie ilints, then we must 

 allow it to be 690 feet thick, leaving little more than 200 lor the Middle and 

 Lower C^halk together. At Landguard Fort, from the same point of view, the 

 Upper Chalk would certainly be 500 feet thick, and one can't say how much 

 more. 



At Combs, on the other hand, flints have been recorded as present only in the 

 top 27 feet of the Chalk ; but whilst this may have been owing in part to the 

 boring having passed between fairly scattered nodules, and in part perhaps to 

 insufficient care in observation, at Harwich it is possible that some ilints may have 

 been carried down in the process of boring. It should be remembered, too, that 

 there are flints in part of the Middle Chalk, so that their presence is not an 

 unfailing guide. 



What evidence we have tends to .show, however, that the Upper Chalk forms 

 a good deal more than half, and perhaps about two-thirds, of the formation, the 

 Middle and Low'^r Clialli being rather thin. This agrees with what is found in 

 other parts where the Chalk is thick, extra thickness being chiefly due to the 

 highest division. The glauconitic marly bed at the base seems to be well 

 developed and to be underlain by the Gault clay ; so that we have no good 

 evidence of the occurrence of Upper Greensand. This division may be thinly 

 represented at Mildenhall, but it is difficult to classify some of the beds passed 

 through in the old boring there. 



As far as the Gault is concerned little of course is known ; but that little 

 pomts to this formation being unusually thin, presumably only 73 feet from top to 

 bottom at Culford, and probably not more than between 50 and 60 at and near 

 Harwich. In the north-western part of the neighbouring county of Norfolk it is 

 well known to be still less, the clay thinning out northward along the outcrop, 

 until at last there is nothing but a few feet of Red Chalk between the carstone of 

 the Lower Greensand and the Chalk. The Gault being of much greater thickness 

 around and under other parts of the London Basin, this thinning in Norfolk and 

 Suffolk is noteworthy. The absence of the more inconstant Upper Greensand is to 

 be expected in most places, and calls for no remark ; it may, however, be noted 



