i86 



HA RD WICKE' S SCIENCE- G OSSIF. 



GEOLOGY, &C. 



Wells in West Suffolk Boulder-Clay. — 

 The following important communication was recently 

 read before the Geological Society by the Rev, 

 Edwin Hill, M.A., F.G.S. It might be supposed 

 that in a boulder-clay district water could only be 

 obtained from above or from below the clay. But 

 in the writer's neighbourhood the depths of the wells 

 are extremely different, even within very short 

 distances ; and since the clay itself is impervious to 

 water, he concludes that it must include within its 

 mass pervious beds or seams of some different 

 material which communicate with the surface. It 

 would follow that this boulder-clay is not a uniform 

 or a homogeneous mass. The visible sections are 

 only those given, at hand by ditches, and at a con- 

 siderable distance north and south by pits at Bury 

 St. Edmunds and Sudbury. The appearances in 

 these harmonize with that conclusion. Conclusion 

 and appearances differ from what we should expect 

 on the theory that this boulder-clay was the product 

 of the attrition between an ice-sheet and its bed. 

 In the discussion which followed, Professor Prestwich 

 remarked that intercalated beds of gravel and sand 

 were common at different levels in the more northern 

 boulder-clay, and that in parts of the Eastern Counties 

 a bed of gravel, from one to twenty feet thick, 

 generally occurred in the centre of the boulder-clay. 

 These formed small water-bearing beds, but the 

 ' main sources were usually at the base of the clay — a 

 base which was extremely irregular. He asked the 

 author how, as the wells stopped at the water- 

 bearing stratum, he could be sure that this was, in 

 all instances, intercalated and not an underlying bed. 

 It was essential to know the level of the ground at 

 the different wells, and this would no doubt be given 

 in the paper. The component beds of the boulder- 

 clay would vary according to the surface passed over 

 by the ice, and may, therefore, include long trails of 

 sands and gravels, and are necessarily local and 

 irregular. He hoped that the author would continue 

 his observations. Dr. Evans agreed with the author 

 in regarding the mixed character of the boulder-clay 

 of Suffolk and some of the features that it presents as 

 being hardly consistent with its being merely the 

 result of a coating of land-ice. In illustration of the 

 permeability of the beds at certain spots, he cited 

 the deep circular pits or meres in the neighbourhood 

 of East Wretham, Thetford, which were due to the 

 dissolution of the underlying chalk by water charged 

 with carbonic acid having forced its way through the 

 clay. The level of the water in these meres depends 

 upon the saturation of the chalk, and the bottom of 

 what in one year was a deep pool might in another 

 year be cropped with turnips. Mr. Clement Reid 

 observed that intercalations of seams of sand were 

 almost universally characteristic of the boulder-clay, 



and helped to render it somewhat pervious to water. 

 He was unable to follow the author's argument, that 

 irregularities in the deposits proved that the boulder- 

 clay could not have been formed under ice. Mr. 

 Topley called attention to the researches upon the 

 glacial geology of the Eden Valley carried on by 

 Mr. Goodchild, who believed (as does Mr. Reid for 

 Norfolk) that the irregular beds of gravel and sand 

 occurring in the clay were formed within or under 

 the ice-sheet, the gravel, &c., having been washed 

 out of the clay into hollows of the ice during partial 

 or local melting of the ice-sheet. Mr. Goodchild 

 said that similar intercalations of sands and gravels 

 in the boulder-clay were common in the north. He 

 reminded the society that he had proposed an ex- 

 planation of the origin of such deposits many years 

 ago in the society's journal and elsewhere ("Quart. 

 Journ. Geol. Soc," vol. xxxi., and " Geol. Mag." 

 for 1874). The president referred to his own early 

 work in the boulder-clay, and the abundant evidence 

 which he had everywhere found of intercalated nests 

 and layers of sand and gravel in that deposit. He 

 had always been accustomed to regard these inter- 

 calations and their singular contortions as affording 

 some of the strongest proofs of glacier action, and 

 though he admitted that the boulder-clay still pre- 

 sented many unsolved difficulties, he had never seen 

 what he could regard as a valid argument against 

 the view that the true typical boulder-clay is essen- 

 tially a product of land-ice. The author, in answer 

 to Professor Prestwich, said that he had taken into 

 account the variations in surface-level of spots where 

 wells existed. Dr. Evans's instances of permeability 

 in boulder-clay were a valuable corroboration. The 

 appearances of sections did not to himself suggest 

 an origin such as erosion by subglacial streams. He 

 would be very glad to study the sections at Saffron 

 Walden and those in the Eden Valley described by 

 Mr. Goodchild. He was not aware of any case in 

 which a "ground-moraine" had been seen in actual 

 process of formation, but he imagined that any 

 structures possessed by a mass so formed would be 

 horizontal in their general direction. The appear- 

 ances described in the paper were not of that 

 character. 



The Geology of the Tonga Islands.— Mr. 

 J. J. Lister read a paper on this subject. The islands 

 of the Tonga group are situated on a long ridge 

 which rises from deep water on either side to within 

 a thousand fathoms of the surface of the sea. The 

 general direction of the ridge is N.N.E. and S.S.W. 

 (i) A line of volcanoes, some active, some extinct, 

 traverses the group. Continued southward, the 

 direction of the line passes through the volcanoes of 

 the Kermadec group, and those of the Taupo zone of 

 New Zealand ; while to the north it cuts the line of 

 tiie Samoan volcanoes at right angles. (2) Besides 

 the purely volcanic islands there are some formed by 



