S. V. Wood,jun. — American and British Surface- Geobgy. 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. 1 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 fresh water 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 excavation 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 necessarUy 
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 olf 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 Flam- 
borough Head, its direction would have been straight towards 
Cromer, around which town for several miles the great masses of 
remaniö 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 remcinie 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. Y. "Wood, Jun., and F. "W. Harmer, in Q.J.G.S., Feb. 1877, p. 74, and 
F. W. Harmer in same, p. 134. 
