S. V. Wood, Jun.— The Fost'Glacial Period. 159 



about this time, of ice conditions adequate to the transport of small 

 boulders, such as is evinced by the remarkable nest of boulders 

 which occurs in the Brick-earth at Grays, in the Eastern Thames 

 valley. 



I have in various papers endeavoured to show that the South and 

 South-east of England was, during the earlier part of the Post- 

 glacial period, covered principally by sea, the bottom of which was 

 undergoing disturbance and great denudation from subterranean 

 action, the country to the North of the Thames being land, and 

 penetrated by small rivers in which these C?/rena-bearing Brick- 

 earths accumulated ; and I have given restoration maps in which I 

 have endeavoured to trace the emergence of the South of England 

 from this stage.^ Now it is remarkable that in all the great sheet 

 of the Thames gravel which preceded this Brick-earth we should get 

 no traces of boulders, while so many should occur in the Brick-earth 

 itself ; and the circumstance seems to me to indicate the absence of 

 ice-action during the deposit of the former, and its commencement 

 during the accumulation of the Brick-earths. Further, in those 

 gravels of Hampshire which, in the paper last referred to, I have on 

 totally different evidence endeavoured to correlate with these 

 Cyrena Brick-earths, boulders of Sarsen sandstone occasionally occur.^ 

 These seem to be confined to the gravels at medium and lower 

 levels, and to be absent from that higher part of the Hampshire 

 sheet which I have attempted to connect with the main and higher 

 sheet of Thames gravel. 



In the same paper, and in the restoration maps accompanying it, I 

 have endeavoured to show that the emergence of the principal part 

 of the South of England, and the retreat of the sea within the 

 Valley of the Weald, the denudation of that valley, and the eventual 

 reversal of the drainage in it, was posterior to these Cyrena Brick- 

 earths of the .Thames Valley, and occupied that long period which I 

 call the later part of the Post-glacial one ; and I also endeavoured to 

 show that the non-glacial Boulder-clay of the Sussex coast, in which 

 very large blocks derived from the West occur, belonged to this 

 later Post-glacial period. I have already pointed out that this clay, 

 like the Hessle, had it been formed during the Glacial period, could 

 hardly have failed to present those physical features which are common 

 to all Glacial-clay formed in the neighbourhood of soft strata, and 

 especially of the Chalk ; and it is most important that it offers in 

 the molluscan fauna of the deposit which it overlies similar cor- 

 roborative testimony of Post-glacial age as does the Hessle clay. 

 Like the latest part of the Crag, all the Glacial beds of the East of 

 England yield some mollusca which are not known living, and 

 others whose present habitat is in distant and northern areas such as 

 the North American coast, Greenland, etc. The oldest of these, the 

 pebbly sand of Norfolk and Suffolk (the shallow water equivalent, 

 as I regard it, of the Cromer Till), has some of both of these classes ; 

 the East Anglian Middle Glacial has this feature even more marked, 



' Quart. Journ. Geol. Soc, vol. xxvii., p. 20. 



^ For some examples see Geol. Mag., Vol. III., p. 296. 



