PltOCEEDINGS OE GEOLOGICAL SOCIETIES. 



59 



at Counter Hill (New Cross), Loam Pit Hill (Lewisham), and very many 

 other places. 



The great shingle-beds of the neighbourhood of Bromley and Black- 

 heath, have been in part classed by Mr. Prestwich, though doubtfully, 

 with the "basement-bed" of the London Clay ; but there is some reason 

 to think that they may all belong rather to the Woolwich beds. In some 

 places, and markedly in the " rock-pit " in Sunderidge Park, near Bromley, 

 and in the rail way- cutting at Beckenham, there are fossils in the pebble- 

 beds ; and it seems strange that many very delicate shells should be pre- 

 served in a loose mass of hard pebbles. 



In some places, as on the hill above Abbey Wood, the shell-beds have 

 thinned out, and there is nothing but sand and pebbles from the top to the 

 bottom of the formation. The pebble-beds, as might be expected of de- 

 posits of that nature, are merely lenticular masses on a large scale, of great 

 thickness at one spot and near by altogether absent. 



Eastward of the valley of the Cra} r , Tertiary formations have suffered 

 much from denudation, and from Dartford to beyond Grravesend are pre- 

 sent only in the form of outliers. The clay shell-beds get thinner, and at 

 the great section on the bank of the Medway, at Upnor, are only 6 feet 

 thick, the sand above, however, also containing shells, but not that below. 



For some way east of Rochester this formation has been almost wholly 

 denuded, but it comes on again west of Sittingbourne. Near this latter 

 place the estuarine shell-beds thin out and are not seen further eastward. 

 The pebble-bed at the bottom is also lost, and it is then difficult to draw 

 the line between the Woolwich beds and the underlying Thanet Sand, the 

 former, however, being mostly a coarser and sharper sand, with here and 

 there a few pebbles. The fossils also of the two formations are more alike, 

 those of the Woolwich beds being here of a purely marine kind, and in 

 great part of the same species as those of the lower formation, but of rarer 

 occurrence. The sands that in East Kent represent the Woolwich beds 

 are 25 to 40 feet thick, and are well shown on the coast west of the Recul- 

 vers, in sections near Canterbury and Ash, and in the railway-cutting at 

 llichborough Castle. 



3. The Basement Bed of London Clay consists, near Lewisham and 

 Bromley, of a more or less clayey pebble-bed, from 3 inches to 2 or 3 feet 

 thick, and is well shown in the large pits at Loam Pit Hill, near the former 

 place. 



Mr. Prestwich classes with this bed, though somewhat doubtfully, the 

 thick wide-spread mass of shingle of Blackheath, Charlton, etc.; but in 

 the railway-cutting, east of Bickley, a sandy pebble-bed, like that of Black- 

 heath, is seen to be overlaid by the usual clayey pebble-bed at the bottom 

 of the London Clay, and it w^ould seem therefore that the thick mass of 

 pebbles in sand at Blackheath, etc., do not belong to this bed ; whether 

 they belong to the underlying Woolwich beds or not, is another question. 



Erom this western part of Kent there are no sections of the " basement- 

 bed " for some distance eastward, and possibly it may have thinned out. 

 At Upnor, near Rochester, however, the whole of the Tertiary beds, from 

 the lower part of the London Clay to the top of the Chalk, are shown. The 

 former is underlaid by some 4 or 5 feet of fine light-coloured sands with 

 shells, in a very friable state, and with pebbles near the bottom. These 

 Mr. Prestwich classes with the " basement-bed," and they certainly so em 

 to be separable from the underlying sands and shell-beds of the Wool wich 

 series, though, on the other hand, they are sharply divided structurally 

 from the stiff London Clay above The fossils in them are, for the most 

 part, of species generally found in the basement-bed (chiefly of the 



