﻿S. V. Wood, Jim. — American and British Surface- Geology. 539 



its recession only. The ice which accompanied the accumulation of 

 the Lower Glacial beds does not appear to have reached so far south 

 as did that to which the chalky part of the Upper Glacial was due ; 

 but after this accumulation a material change took place, and 

 extensive troughs were excavated through these beds, which were 

 filled in by the Middle and Upper Glacial deposits.^ These troughs, 

 by their re-excavation, have in great measure originated the present 

 valley-system of East Anglia, part of such re-excavation having been 

 produced by the advance along them of tongues from the inland-ice 

 during the formation of the chalky clay, as presently explained. 



At the bottom of one of these filled-in troughs, which has not 

 been re-excavated, lies the Kessingland freshwater formation with 

 some arboreal remains and a root-penetrated surface, covered evenly 

 by the Middle Glacial sand. Whether this formation is a deposit 

 in the trough, and therefore of interglacial age, or whether it is a 

 preglacial formation which the excavaticJn of this trough through 

 the Lower Glacial beds uncovered without destroying, is a question 

 for the determination of which no sufficient data have yet been 

 detected. If, however, this formation should prove to belong to 

 the period of interglacial trough excavation, it would not necessarily 

 indicate an amelioration of climate, because, according to Milner's 

 Atlas, forests in Norway, and according to Von Wrangel's Map, 

 forests in Siberia extend many degrees of latitude north of that 

 parallel (61° N.) down to which glaciers give off bergs in South 

 Greenland. 



The glacier, the accretion and extension of which accompanied 

 the accumulation of the Lower Glacial beds, was, I think, most prob- 

 ably that of the Yale of Pickering, to which I shall in the sequel 

 have occasion to refer in connexion with the Purple clay. If this 

 glacier deflected south-eastwards over the Chalk along the line 

 marked by the Purple clay, which caps the Chalk towards Plam- 

 borough Head, its direction would have been straight towards 

 Cromer, around which town for several miles the great masses of 

 remanie Chalk are imbedded in the Contorted Drift. From Flam- 

 borough southwards this glacier would have travelled exclusively 

 over Chalk, and terminating at some point between Flamboro' and 

 Cromer, where the water was deep enough to generate them, would 

 have sent off bergs laden with masses of remanie Chalk, which, 

 grounding near Cromer, buried them in the marine silt, and gave 

 rise to the contortions which accompany these masses, and to which 

 this Silt or Drift owes it name. The elevation of the Lower Glacial 

 sea-bed over Norfolk and Suffolk, which put an end to the accumula- 

 tion of the Contorted Drift, reduced, it is probable, this depth of 

 water and put an end to the generation of bergs by the Pickering- 

 glacier, so that a new state of ice arrangement resulted. Whether 

 the outflow of this glacier was checked by an elevation of the sea- 

 bottom, or merely by the great accumulation of sediment to which it 

 gave rise, such a change in relative levels of the places of least resist- 



1 See S. V. Wood, Jun., and P. W. Harmer, in Q.J.G.S., Feb. 1877, p. 74, and 

 F. "W. Harmer in same, p. 134. 



