1868.] WOOD PEBELE-UEDS. 465 



rest, with a well-defined line of division, and somewhat unconform- 

 ably, upon tho Lower Bagshot Sand ; but sometimes they appear to 

 be interbedded with the upper part of that sand itself. Although 

 the Glacial Clay is in several parts in the closest contiguity to these 

 beds, the two have obviously no connexion with each other, since the 

 former lies u]) against the pebble-beds, and occupies slight depres- 

 sions eroded through them, as at Pilgrim's Hatch in the accompany- 

 ing section. Nothwithstanding their close contiguity to the Glacial 

 Clay, the pebbles never rest ujpon it, and are thus shown not to be of 

 Postglacial age ; while their constituent material, rounded condi- 

 tion, and places of occurrence equally remove them from any con- 

 nexion with the Middle Glacial Gravel. These features, found to be 

 constant over all the tableland on the north of the Thames, have for 

 several years past induced me to regard the beds in question as not 

 improbably of Eocene age, and, from their invariable association 

 with the Lower Bagshot Sand, as having belonged either to the close 

 of that formation, or else as representing in these parts the Middle 

 Bagshot of Surrey. In either case their bearing upon the geogra- 

 phical changes during the Eocene period would be the same, since 

 they would thus indicate that the final recession of the Eocene sea 

 from Middlesex and Essex was coeval with the commencement of 

 the rich fossiliferous marine, estuarine, and freshwater series of 

 Hampshire, which, geologists seem agreed, took place at the close 

 of the Lower-Bagshot period. 



The association of these pebble-beds with this event, however, is 

 only a provisional one, and one adopted for want of some satisfactory 

 evidence of the occupation of Middlesex and Essex by the sea 

 between the Lower-Bagshot- Sand period and the Glacial. The 

 principal point connected with these, to which I desire to call atten- 

 tion, is their disconnexion with the gravels either of the Glacial or 

 Postglacial series, and more particularly their distinction from the 

 gravel, principally made up of pebbles (but of which many are 

 broken), that underlies the Glacial clay at high levels, lately described 

 by Mr. T. M'K. Hughes as " Gravel of the Higher Plain of Hertford- 

 shire." 



If the evidences upon which Mr. Prestwich relies as indicative of 

 the denudation of the Eocene Tertiaries over a portion of Kent, and 

 the occupation of that denuded area by the sea during the period of 

 the Coralline Crag, or of some anterior part of the Diestien Series, 

 were sufiiciently unequivocal to justify us in assuming that the 

 Coralline Crag, or some yet older Pliocene, or some newer Miocene 

 sea washed a dome of chalk protruding through the lower Ter- 

 tiaries, we might associate the pebble-beds which thus invariably 

 accompany the Lower Bagshot outliers with such a geographical 

 feature, and refer them to the older Pliocene, or newer Miocene 

 period. We may fairly assume such an age as one of the possi- 

 bilities connected with them ; for the somewhat unconformable posi- 

 tion which the pebbles occupy relatively to the Lower Bagshot on 

 which they rest would assist their separation from the Bagshot 

 series ; and could the presence of the sea over Kent during the Dies- 



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