On the Late Glacial Stage of the Lea Valley. 413 



mineral composition over wide areas, and in deposits lithologically 

 different. The mineral suite of the succeeding Pliocene beds 

 (with abundant red garnets, andalusite, mica, and ferromagnesian 

 minerals) is shown to be very different, and the constituents of 

 various other East Anglian deposits are also compared. 



In the Thanet Beds, ferromagnesian minerals are present and 

 undecomposed, the micas being rare. In the shallow waters in 

 which the Reading Beds were deposited, the biotite. hornblende, 

 pyroxene, and epidote appear to have been largely lost, aided no 

 doubt by current-drift along a shore. The Pebble-Beds show 

 occasionally natural concentration of heavy minerals by oscilla- 

 tory current-action. In the subsidence which followed when the 

 London Clay was deposited, muscovite and biotite appeared in fair 

 quantit}^, and hornblende became abundant. Such minerals as 

 magnetite, ilmenite, rutile, zircon, glauconite, etc., are plentiful 

 throughout. 



April 14th.— Dr. A. Smith "Woodward, F.K.S., President, 

 in the Chair. 



The following communication was read : — 



' Further Observations upon the Late Glacial, or Ponder's End, 

 Stage of the Lea Valley/ By Samuel Hazzledine Warren, F.GLS. 

 With Notes on the Mollusca by Alfred Santer Kennard, E.G.S., 

 and Bernard Barham Woodward, F.L.S., F.Gr.S. 



The paper is supplementary to that previously published 

 (Q. J. Gr. S. vol. lxviii, 1912, p. 213), and describes additional 

 sections which increase the range of the deposits. They have now r 

 been traced, with the assistance that the author has received from 

 Mr. A. Wrigley, for a distance of 6| miles along the valley and 

 1\ miles across it. The section at Hedge Lane, Lower Edmonton, 

 shows several thick, and for the most part undisturbed, Arctic 

 plant-beds, which occur in a deep Drift-filled channel. The relative 

 levels and stratigraphy point to the conclusion that the Hedge 

 Lane deposits belong to a slightly earlier stage of the Low-Terrace 

 River-drift than the deposits of Ponder's End. Broadly speaking, 

 they undoubtedly belong to the same group. 



The author suggests that it would be a practical convenience if 

 the East Anglian word ' platymore ' were adopted for the under- 

 lying eroded floor of country-rock beneath a later accumulation of 

 drift. The importance of this ' platymore ' surface in the corre- 

 lation of Drift deposits has been increasingly recognized during 

 recent years, and it seems desirable that it should have a name. 



The author supports the correctness of the view that the lower 

 river-terraces are later than the higher river-terraces. Further 

 evidence is also brought forward in support of his view that the 

 Arctic deposits form an integral part of the Low-Terrace Drift : 



