668 REPORT— 1895. 



as ia such places it rarely reaches a tliickness of 40 feet. But, on the other hand, 

 wells at Hoxne seem to prove more than 60 feet of Crag, whilst at Saxmundham 

 the formation is 100 feet thick, and at Leiston and Southwold over 140. Further 

 north, just within the border of Suffolk, there is, at Beccles, a thickness of 80 feet 

 of sand, or, with the overlying Chillesford Clay, a total of 95. Our underground 

 information has, then, trebled the known thickness of the Upper Crag of Suttblk. 



It has also shown that at some depth underground the colour-name is a mis- 

 nomer, the shelly sands being light-coloured and not red. This is the case too 

 with some other deposits, which owe their reddish-brown colour at the surface to 

 peroxide of iron. Presumably the iron-s.alt is iu a lower state of oxidation until it 

 comes within reach of surface-actions. This seems to point to the risk of taking 

 colour as the mark of a geologic formation. 



Eocene Tertiaries. 



Below the Crag there is a great gap in the geologic series, and we couie to 



some of the lower of the Tertiary formations, about which little liad been 



published, as regards Suffolk, before the work of the Geological Survey in the 



'county. It seems as if the special interest in the more local Crag had led 



observers to neglect these lieds, which had been amply noticed in other parts. 



We have records of more than forty wells in Suffolk that are partly in these 

 deposits, and of these thirty-six reach down to the Chalk, twenty giving good 

 sections from the London Clay to the Chalk. The thickness of the Lower London 

 Tertiaries (between those formations) thus proved varies from 30 to 79i feet, the 

 higher figure being much greater than anything shown at the outcrop. The 

 greatest recorded thickness is at Leiston, where, moreover, the top 26 feet of the 

 79^ may belong to the uppermost and most local of the three divisions of the 

 Series, the Oldhaven Beds, of very rare occurrence in tlie county. The next 

 greatest thickness is at Southwold, where the whole has been classed as Reading 

 Beds (the persistent division), though here and elsewhere it is possible that the 

 underlying Thanet Beds are thinly represented. It is noteworthy that at both 

 these places, whei'e the Lower London Tertiaries arc thick, they are also at a 

 great depth, beginjiing at '2b2h and 218 feet respectively, which looks as if, like 

 the Crag, they thickened in their underground course away from the outcrop. 



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

 ness; it is to show the undergi'ound extent of the older Tertiary beds, beneath the 

 great sheet of Crag and Drift that prevents 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 oft' 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 Southwold the Chalk would not be touched till a boring had 

 reached the depth of 323 feet, or some 280 below sea-level, or that at Leiston 

 those figures would be 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 irregularitj' in the 

 thickness of the Drift, it is clear that this line must be taken only as approximate, 

 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 toward the coast. 



Cretaceous Beds. 



Though the Chalk is reached by very many wells, yet we 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. 



